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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
Need help w/ surging idle... The Parent Thread has an updated vid where the surging idle nearly vanished... When I first started it would idle under 750 rpm i believe, when placed in gear it dropped to the 400-500 rpm range and begins idling as shown below. It'll hunt and once it finds it's groove it idles high between 1500 - 2K rpm. I've cleaned the IAC but it didn't have a noticeable impact.
Btw, what is the stock idle RPM on a 92rs 305 TBI? If a battery is dead (or disconnected) how long before complete memory loss and things like IAC re-learn need to be completed? If higher than normal idle and bogging / stalling when placed in gear are indications of a vac leak what are your best practices on locating it? Any advise would be appreciated.
What is the stock idle RPM on a 92rs 305 TBI?
If a battery is dead (or disconnected) how long before complete memory loss and things like IAC re-learn need to be completed?
If higher than normal idle and bogging / stalling when placed in gear are indications of a vac leak what are your best practices on locating it?
Any error codes like code 24 for Vss ?
Idle speed I thought was higher like 650 but the tune says 525.
A small vacuum leak would cause a high idle. Have you checked injector spray pattern to see if they are dripping ?
You can point a timing light hooked up to cylinder number one and aim it at the injectors to see the spray pattern. It should be a nice cone shaped pattern. No dripping. I would try to set the minimum idle speed with the iac commanded in to 650 rpm. Disconnecting the battery will erase codes after 15-30 min maybe even less. No need to do a iac minimum setting for just disconnecting the battery.
Any error codes like code 24 for Vss ?
Idle speed I thought was higher like 650 but the tune says 525.
A small vacuum leak would cause a high idle. Have you checked injector spray pattern to see if they are dripping ?
You can point a timing light hooked up to cylinder number one and aim it at the injectors to see the spray pattern. It should be a nice cone shaped pattern. No dripping. I would try to set the minimum idle speed with the iac commanded in to 650 rpm. Disconnecting the battery will erase codes after 15-30 min maybe even less. No need to do a iac minimum setting for just disconnecting the battery.
Any error codes like code 24 for Vss? No Codes. A small vacuum leak would cause a high idle, Any suggestions on locating it safely? Have you checked injector spray pattern to see if they are dripping? Yes, I thought I saw a drip/dribble come from one. I'll have to check again after work.
To set the min idle speed, i see that cap is no longer over the screw on my TBI like it's been tampered with... the IAC and TPS appear to have been replaced. Can I just turn the screw w/ the engine running to adjust?
If you have a scanner you can watch iac steps and engine warm set it to 20steps.
otherwise you need to ground the aldl a to b with the key on.Disconnect the iac connector and start the engine then adjust the stop screw.
to find a vacuum leak you can use propane torch unlit or carb choke cleaner. Keep the carb chock cleaner spray away from the exhaust manifolds. The tbi base gasket is a common point for a vacuum leak. As for the injectors if one has a small dribble the egine might run alittle rich and rough idle.This could also be a ignition problem your fighting like a bad icm.
No scanner, I have a post out looking for on here. As far a fuel spray pattern the vid is below. Going out to work on trying to set the minimum idle speed to 650 rpm.
EDIT: Did the idle speed set control, good news... I know how to set the minimal idle. I adjusted it down from the 1500+ to about 700ish RPM's based on gauge. When I went as low as the mid 500's she about died... even set at 700ish RPM the slow yet surging idle remains. I also noticed if I gave it some gas it sounded like the TB was sucking in huge amounts of air, she nearly bogged out.
EDIT: *If anyone has viewed this vid, do the injectors seem leaky?
Last edited by 92RS-HeritageEd; 03-29-2019 at 10:11 PM.
to find a vacuum leak you can use propane torch unlit or carb choke cleaner. Keep the carb chock cleaner spray away from the exhaust manifolds. The tbi base gasket is a common point for a vacuum leak. As for the injectors if one has a small dribble the egine might run alittle rich and rough idle.
Seen a YouTube vid where a guy blew cigar smoke in through a vac line to find leaks. Ever tried this? It seems safer on a novice over the Propane or Carb/Choke cleaner...
Doing the best I can following the GMSM continuing troubleshooting up until the arrival of my ALDL cable...
1. *If* I had a smoke machine, what vac port would it get connected to, the MAP vac line that connects to the intake? EDIT: Tried the cigar smoke YouTube method... all smoke pumped in just came out of the TBI Unit. Tried the vac line off the MAP, tired the vac line from the T-Fitting at font of the DS finder that runs up to another T-Fitting and into the intake. Same result, smoke only straight up and out of the TBI. Nothing around the EGR, base of TBI, or intake...
2. Does Open Loop vs Closed Loop play a part in this? Can a "going bad" o2 sensor cause this from a cold start? The ECM doesn't have and has never thrown or stored any codes, it does flash 12 at key in run position. I thought the only time a o2 sensor even mattered was in closed loop operation.
3. Since there's no reliable ICM test, and it's a possibility, throw one at it? EDIT: Since there's no reliable ICM test, and it's a possibility I ended up buying a used Kent Moore J-24642 High Energy Ignition Module Tester GM Specialty Tool.
4. Could this be caused by "straight piping" and pinching off that AIR tube that went to the cat from the smog stuff as was done by the P.O?
Last edited by 92RS-HeritageEd; 03-29-2019 at 09:57 PM.
Couple other things you can check to see about leaks.
hook up a vag gauge.
take a can of MAF cleaner and when it starts stalling put just a tiny spritz in there. if the idle just right up and it seems to recover from the squirt you have a lean run condition. If that **** just goes "oh hell naw" and then dies on you the moment you squirt it in then you are running rich.
hold your hand in the exhaust stream then sniff it.. how does it smell, clean, gassy, sweet, or maybe like Tuned Performance's *** right after he dropped deuces?
you can test wires by pulling one at a time to see if it runs consistent without bouncing up and down. It's going to run rough with 7 out of 8 cylinders, but should at least run without bouncing up and down. if it's running "smooth" then put the wire back and move to the next.
bit of advice, don't pull wires while the car is running. If you decide not to listen to the advise touch it to your tongue then as that will really test the conductivity.
It's been forever so I can't remember, L03 is TBI and is ran off a MAP correct? if it is ran off a MAF instead then clean that bastard off.
Find rubber chicken, put it in your bum and dance around for 30 min. No it won't fix your car, but it might get the attention of someone who might also have an idea. Serious if you saw a dude dancing with a chicken in their bum wouldn't it get your attention ?
my guess it's going to be something air/fuel related though. Too much air going in, or too much fuel going in.
Couple other things you can check to see about leaks.
hook up a vag gauge.
take a can of MAF cleaner and when it starts stalling put just a tiny spritz in there. if the idle just right up and it seems to recover from the squirt you have a lean run condition. If that **** just goes "oh hell naw" and then dies on you the moment you squirt it in then you are running rich.
hold your hand in the exhaust stream then sniff it.. how does it smell, clean, gassy, sweet, or maybe like Tuned Performance's *** right after he dropped deuces?
you can test wires by pulling one at a time to see if it runs consistent without bouncing up and down. It's going to run rough with 7 out of 8 cylinders, but should at least run without bouncing up and down. if it's running "smooth" then put the wire back and move to the next.
bit of advice, don't pull wires while the car is running. If you decide not to listen to the advise touch it to your tongue then as that will really test the conductivity.
It's been forever so I can't remember, L03 is TBI and is ran off a MAP correct? if it is ran off a MAF instead then clean that bastard off.
Find rubber chicken, put it in your bum and dance around for 30 min. No it won't fix your car, but it might get the attention of someone who might also have an idea. Serious if you saw a dude dancing with a chicken in their bum wouldn't it get your attention ?
my guess it's going to be something air/fuel related though. Too much air going in, or too much fuel going in.
- Don't have a vac gauge but can grab a HF el-cheapo and yes the L03 is TBI and is ran off a MAP.
- Testing is important, but I will not pull wires while the car is running. No worries about me deciding not to listen to the advice, I'm no remedial dumb @$$ and this isn't a 9v battery so anyone who touches it to their tongue to really test the conductivity should forfeit their car.
- Exhaust smell... it smelled clean i suppose not "gassy, sweet, or maybe like Tuned Performance's *** right after he dropped deuces?" Btw how'd you know about the smell of "Tuned Performance's *** right after he dropped deuces"????????????????
- Find rubber chicken, put it in your bum and dance around for 30 min. Heck no buddy that won't fix my car, attention or assistance isn't needed that bad lol
A neighbor of mine did swing by and he stated it looked like my injectors were dumping fuel, idk but will know more once my cable arrives. All in all, thanks for the info and laughs rx7speed.
This could also be a ignition problem your fighting like a bad icm.
Connected spark checkers from Cap to Coil & at SP#1... when the surge starts to happen the light at the Cap/Coil connection is faint and the light connected at SP#1 is blinking. Does this confirm the ICM?
When it’s not surging is the spark brighter ?
Are you using a 40kv tester ?
Light at the Cap/Coil is faint period, I didn't notice the faint light blinking at sp#1 until the surging started. The testers are Harbor Freight item numbers 69023 & 63846 and I do not see 40kv on the packaging anywhere.
I don’t see the specs on harbor freights site. You should still have a hot spark not weak. Do you have another vehicle to test the spark tester on to see the difference?
possiable causes icm , coil and maybe the pickup coil.
I don’t see the specs on harbor freights site. You should still have a hot spark not weak. Do you have another vehicle to test the spark tester on to see the difference?
possiable causes icm , coil and maybe the pickup coil.
I used this set of testers last year when diagnosing a random no start condition on my main 92rs. They worked on diagnosing a bad ICM then. I swapped in another ICM. Car started as it did before, the light at the Cap/Coil seems stronger and flashes no longer seem weak or inconsistent w/ RPM. Thinking about the afr route and possibility of injectors staying open to long? They just seem to be dumping fuel (as told by a neighbor) but no ones chimed in on the video above so I really don't know.The fuel pressure at the fuel filter is 12/13psi consistent and doesn't drop when the surging starts, can't get the other adapter behind the TBI to test fp there.
- Because this happens within 400 sec of startup would I be troubleshooting afr from an Open Loop perspective where I should test the tps, cts & map?
- In TunerPro the Closed Loop Timer is 400 sec. Does that mean within 400 seconds the coolant temp should be about 123F (Minimum for Closed Loop) and the signal from the o2 sensor should determine afr and how long the injectors stay open?
Installed new cts before last post and issue remained. Moving onto tps... at key on engine off it read 1.097 volts. The GMSM says the tps signal voltage will vary from about .5 at idle to about 5 volts at wot but then states with ignition on or at idle the tps signal should be less than 0.95 volts. I'm confused. Is the tps bad or is 1.097 volts within range even though it's double the .5 rough baseline?
EDIT: Simple research is indicating that any messing w/ the IAC & the speed set screw also requires readjustment of the tps. I found a write up under the how to's. Wonder if the ECM will quit dumping double the fuel since tps is reading 1.097 vs .5 and resolve this issue, I'll see.
Last edited by 92RS-HeritageEd; 03-31-2019 at 11:06 PM.
Low fuel pressure is the usual cause of low idle RPM and surging with TBI.
The fuel pressure at the fuel filter is 12/13psi consistent and doesn't drop or fluctuate when the surging starts or during, this is shown in one of my above videos. I've also swapped pumps much earlier on as I though it was a low fuel volume issue, no luck...
Interesting article I found here implied on newer 3rd Gen's that the TPS isn't actually adjustable, it's adjustment comes with setting the minimum idle which differs from the information in the How-To's..
So I'm feeling like a fish out of water here, no mater what I do I get code 33 MAP signal Voltage High - Vacuum Low. I've tried...
- Every Step mentioned in the GM Service manual.
- FPT w/ consistent reading on 11/12psi.
- Swapped 2 or 3 different MAP Sensors w/ new Vac Line.
- Attempted Idle Speed Set.
- Swapped Alternators.
- Swapped ECM's/PROMs.
- Swapped TBI Bases - Base unit had un-tampered Idle Set Screw w/ IAC & TPS pre-installed, Bolts torqued to spec.
- Replaced Gaskets at TBI Base also between TBI Base & Injector Pod.
- Sprayed carb cleaner around base gasket, I couldn't detect a leak.
* Side By Side comparison of Datalogs - TPS voltage now right in line w/ my running 92rs. MAP voltage... through the roof. IAC position is also much higher than my running 92rs.
- Connected a Vac Gauge between MAP & port on TBI. As I let off the gas the gauge rocks in between 5-10 and when I hold the gas it struggles to stay in the 13-15 range, only went into the green for a split second while giving it some gas.
My questions at this point are
- What exactly makes up Manifold Absolute Pressure?
- Could this be a timing issue?
- How do you check for leaks in the Intake Manifold?
- What do the difference in the IAC counts mean?
Last edited by 92RS-HeritageEd; 04-08-2019 at 07:36 PM.
Timing will effect engine vacuum, worm engine rings/ valve guides will effect it as well as camshaft.
The iac is a controlled vacuum leak. At 20 or so steps you should be idling at 650 spec.
higher than 20 steps the engine rpm should be higher this is at idle.
Im not sure why one log is higher count than the other. Maybe someone else has a idea. Have you done a compression test on the engine ?
Timing will effect engine vacuum, worm engine rings/ valve guides will effect it as well as camshaft.
The iac is a controlled vacuum leak. At 20 or so steps you should be idling at 650 spec.
higher than 20 steps the engine rpm should be higher this is at idle.
Im not sure why one log is higher count than the other. Maybe someone else has a idea. Have you done a compression test on the engine ?
Log on left is my running 92 and the right is the project car which at it's lowest had a IAC position of 89 but rpm's were only at 625.
Not sure if timing is correct, I do recall seeing some yellow paint on this groove in the HB. I don't have a timing light.
Have not done a compression test, do not have a compression test kit.
What does a camshaft do? Can I tell with a visual if one has been installed?
Log on left is my running 92 and the right is the project car which at it's lowest had a IAC position of 89 but rpm's were only at 625.
Not sure if timing is correct, I do recall seeing some yellow paint on this groove in the HB. I don't have a timing light.
Have not done a compression test, do not have a compression test kit.
What does a camshaft do? Can I tell with a visual if one has been installed?
A camshaft opens and closes the valves. You can measure the intake and exhaust lift at the rocker to tell lift. Duration you would need to install a degree wheel. The other way to tell is to pull the timing gear and lol at the cam numbers to see if it’s stock or not.
What's the Vac reading supposed to be w/ Engine off? Is this even a test?
Like if I connect a vac pump to the vac port on the rear of the intake and not the port on the TBI running to the map. To see if the Intake holds vacuum...
Idk how I missed this but it was probably lack of experience... Started car, forced warm up by holding at 1100ish RPM's eased off the gas and she held her own so I started a log. While logging I ran in and grabbed the carb cleaner gave her a LIBERAL spray around the entire base of the TBI, at the rear as the carb cleaner pooled... I could SEE it being drawn up into the intake or TBI and the idle speed increased, and dropped as the CC dried up.
Problem: The TBI Base gasket shape doesn't match the contour of the intake...
Replaced both o-rings, put gasket sealer on the bottom of the TBI and seated the gasket on the TBI. lathered up the intake mounting surface with gasket sealer, bolted everything up and let it sit for a few. Started her up, CHECKED for leaks, started a log... even drove around the block about 5 times while logging. She didn't stall/die until the 5th lap, while in reverse backing into the driveway. I got a d@amn code 44 at some point, and despite the high MAP voltage from time to time the Code 33 didn't pop.
Do you have any exhaust leaks on the drivers side ?
was the rtv you used o2 sensor safe ?
There's a probable exhaust leak can't say it's on the driver side through. Where the y-pipe forms the Y had some rust through as did the seams of the welded section of straight pipe. The rtv? I used something called VersaChem Gasket Sealant.
The code 44 for lean exhaust is most likely caused by one or more of the following: O2 sensor wire - Sensor pigtail may be mispositioned and contacting the exhaust manifold. Check for an intermittent ground wire between connector and sensor. Poor ECM to engine block ground. Vacuum leaks can cause a lean condition and/or possibly a high idle. Check for cracked hoses a bad gasket or a faulty EGR or PCV Valve. fuel pressure - system will go lean, if pressure is too low. It may be necessary to monitor fuel pressure while driving the car at various road speeds and/or loads to confirm. Clogged injector or lean injector
fuel pressure - system will go lean, if pressure is too low. It may be necessary to monitor fuel pressure while driving the car at various road speeds and/or loads to confirm.
Just remembered I left the fp test adapter in place of the fuel filter. The hose is not long enough to test fp while driving. Can't I just give it some gas and see if the pressure drops or is the fuel demand different under load? Also, If a car has sat w/out a battery or a ECM is pulled off the shelf for use how long does it take the ECM to relearn driving patterns?
The ecm will start to make corrections in closed loop.
Since your pump is new I’m not thinking it’s your problem.
The o2 voltage and high blm really indicate your lean.
I noticed if I did little spritz's of Carb/Air Intake cleaner through the snorkel after like 3 spritz the car idles around 1000 rms's w/ hunting that's barely noticeable. That's also only after coolant temp is above 100F, anything below that is rough. O2 sensor voltage in this log didn't stay below 250 mV for 50 seconds and it's flagged because I didn't clear codes. I've driven my other 92rs w/ code 44 for 2yrs, whatever's driving up MAP voltage on this car is truly holding me back. Also reconnected the vac gauge, it held at 15 (Lateing Timing?!?) while running smooth, but the gauge says 20 is optimal.
So I've just been racking my brain. As stated above today it held vac at 15 (Lateing Timing?!?) while running smooth, but the gauge says 20 is optimal. I started googling lateing timing and it broke down to Late Ignition Timing. I know nothing about timing and am intimidated to even open the new timing light i picked up.
- Does this mean the vac gauge is saying my timing isn't advanced enough? - How does timing impact Open vs Closed loop operation?
Set the timing with the engine warmed up.
disconnect the est connector by the a/c housing it’s a tan/blk stripe wire.
The spec for timing is tdc .
Low but steady gauge reading: late timing, low engine compression, throttle body, or intake gasket leaks.
Im not sure what the normal vacuum reading for your engine is but 20 sounds right.
Set the timing with the engine warmed up.
disconnect the est connector by the a/c housing it’s a tan/blk stripe wire.
The spec for timing is tdc .
Low but steady gauge reading: late timing, low engine compression, throttle body, or intake gasket leaks.
Im not sure what the normal vacuum reading for your engine is but 20 sounds right.
Warmed engine to 195ish > Shut Off > Disconnected EST Wire > Started car
IF i'm reading this right, the painted groove in the HB lines up w/ the flashes but the grove is at the farthest right position. Not in the 1st groove to the right BUT the outter ledge slope of the first notch in the timing tab. Is this bad? EDIT: It's prob bad...
5 or 6 degrees retarded minimum. W/ the EST wire disconnected the ECM does no advancing, right? At what point from crank to fully warm closed loop op does the ECM actually begin advancing timing?
Force warmed engine to 195F > Shut car off / Disconnected EST Wire & connected Timing Light. > Same surging and rough idle nearly stalling until around 6 degrees advanced and idle smoothed out > Shut engine off and disconnected battery. Tightened down DHDB, Rechecked timing, still smooth at 6 degrees. Shut car back off. > Waited 5 min > Connected EST Wire > Connected Battery > Started car. Idle settled out at about 1000 rpm and NO hints of surging.
Of course I took a few laps around the block. MUCH BETTER, no stalling in reverse as I backed into the driveway either! Idk if I didn't tighten the DHDB enough because at the end of my log, already parked and ready to call it quits, it started behaving like it retarded again and I believe I can see it (direction of the ICM) has moved again at some point in the test run. So I'll try again tomorrow.
The overall Successes have been that once it did hold a 6 degrees advanced timing position, at idle all voltages seemed to be inline with my running 92RS w/out codes. Also i had the vac gauge connected and it held 18IN/Hg showing normal motor operation! This left one MAJOR question...
- What STOCK L03 305 TBI requires at minimum 6 degrees advanced to run at minimal smoothness?
Last edited by 92RS-HeritageEd; 04-11-2019 at 07:23 PM.
Slipped balancer, aftermarket cam . I’m not sure if slack in the timing chain can effect this either.
since timing isn’t bouncing around with the est disconnected I wouldn’t think it’s a chain issue.
Slipped balancer, aftermarket cam . I’m not sure if slack in the timing chain can effect this either.
since timing isn’t bouncing around with the est disconnected I wouldn’t think it’s a chain issue.
Idk, it's a tight fit even w/ the crowfoot. I really might not have tightened the hold down bolt to torque spec in the rush of noob excitement. i"ll repeat tomorrow morning after I exchange my timing light.
I did find a guy on YouTube (carguychris85) whom implied "Most of these engines run better with a little more advance. My old G20 van with a TBI 305 that had headers, exhaust, and an edelbrock intake liked 6°BTDC. The TBI heads like 26-30°BTDC at WOT. The factory ECM provides 20-22° BTDC at WOT. Most of the factory timing maps run negative advance numbers at WOT and lower rpm. I have run many of these setups and they ALL liked 4-8° BTDC. "
But for one thing, the latest data seems to show you never get into closed loop. Have you checked the O2 sensor?
I haven't. "TP" might even have mentioned that O2/CL thing in one of my datalogging specific threads. I hate thinking about the O2 sensor. It's far beyond a PITA to remove. I've been trying for 1yr to get the one out of my other ThirdGen for replacement.
03-23-2019, 02:00 PM
but it was probably lack of experience... Started car, forced warm up by holding at 1100ish RPM's eased off the gas and she held her own so I started a log. While logging I ran in and grabbed the carb cleaner gave her a LIBERAL spray around the entire base of the TBI, at the rear as the carb cleaner pooled... I could SEE it being drawn up into the intake or TBI and the idle speed increased, and dropped as the CC dried up. 
I believe I can see it (direction of the ICM) has moved again at some point in the test run. So I'll try again tomorrow.