I replaced my fuel injectors with the Bosch III from Southbay a few months ago. Car starts and runs fine for a bit, but then after it warms up the idle will be around 600 and when I drop it into gear from P to D, D to R, or R to D the idle will drop to 500 rpms and then just die. Car starts and drives fine other than that. Sometimes I can be idling in D with my foot on the brake and it will do the same thing, the car will immediately start back up and drive so long as the idle is high enough so that when I drop it into gear it doesn't fall below 500 rpms and die.

This seemed to happen after I changed out the injectors but also after a wheel brake cylinder popped and I lost my rear brakes. I fixed the rear brakes and also checked the Brake Booster check valve works good only sucks.

I have checked the following.
Fuel Pressure is great (42 cranking/prime, 38 idle, and goes up with throttle to 42-45), but mysteriously the fuel pressure will instantly drop after I turn the engine off. It doesn't hold fuel pressure in the rail. My understanding this can be normal with some fuel pump replacements.

I replaced the IAC valve, the old one looked fine, and the new one didn't fix it.

I checked the Throttle Position Sensor Voltage and it was at .54 so it is good.

For testing purposes as it seems to be and idle problem, I took off the cap on the back of the idle air screw on the throttle body and adjusted the idle up by turning the set screw until the idle was like 900...still drops to 500 when put into gear and then dies.

The only time it doesn't die after it is warm (when dropping into gear) is when I disconnect the brake booster vacuum line to the intake. Then it has no issue as it has enough vacuum, when I reconnect the brake booster vacuum line to the intake the idle drops back down, and when I drop it into gear the idle falls too low and dies. Again car will start up fine, drive and will not die so long as I feather the throttle to keep the idle up a little when I drop into gear.

What the hell could it be lol. Could the injectors be off a little and not idling correctly when there is a vacuum change? Could the FPR be bad? It wasn't doing this prior to me changing out the injectors. The reason I changed out the injectors was because the car kept dying and it ended up being a faulty ignition coil that said Made in China, not the OEM injectors I replaced. They all checked good OHM wise. The OEM injectors were 16 ohms, the Bosch are all 14 ohms. So there is an ohm difference between the Bosch and OEM Delphis.

I will most likely put the OEM injectors back in and see if the issue resolves but thought I would check for ideas prior to doing that in case I am missing something.

 

Stuck the OEM Delphi's back in this morning and still have the issue. Can't figure it out...I guess I will check the plugs next and explore getting an adjustable FPR. Any way to tell if other sensors are the culprit, TPS, ECS, or Oil Pressure Sensor?

 

Do you have a data logging cable? Have you checked MAP voltage, etc while the event described is happening?

 

I don't have a data logging cable (yet) but did just finish driving the car and it ran fine over 40 miles as long as I didn't shift it out of gear (D to R, or R to D). I heard the fuel pump making noise (it was hot 100* today) but with over a quarter tank it sounded like it was struggling and whining like weak pumps sometimes do. I decided to put the fuel pressure gauge on the rail and was surprised to see that the running fuel pressure (engine running hot) looked like it was 35-37 psi, when I blip the throttle from idle and hold @ 2500 rpms it spikes to 42 psi but it drops back to around 35-37 psi. Not sure it should be that low?

I'm now suspecting it is the fuel pump, but was wondering if the fuel pump regulator/diaphragm might be shot. Reason being is that when I turn the key on and prime (don't start the engine), the fuel pressure primes to 45psi but then instantly drops to 0-10psi...so it isn't holding at the rail after the prime cycles. My understanding is that this isn't as big a deal so long as the fuel pressure is good while operating. But I have always been used to the rail holding pressure after prime at least overnight. I know it's not stuck fuel injectors because it did the same thing with the Bosch III injectors I just took out.

Thoughts?

 

If it was a weak pump, you'd have other driveability problems when the fuel demand is much greater than at idle.

You said you ran Bosch-III's and then noticed the problem. Those are notorious for needing chip recliabration to run right (even with the same advertised flow rate)... often times the ECM is detecting them running leaner and is trimming the fuel richer to compensate.

If you ran it for a while with those, what I'd recommend is unplugging the ECM to clear the memory, then running again with your delphi's (since you already have them back on the car). The long term fuel trim (BLM) may have sufficiently adjusted to the Bosch-III's that when you put the delphis back in and the problem repeated right away it could have been getting influenced by the earlier fuel trim.

If the problem goes away at that point, then you know it's what I just described. At which point, you can run the Bosch-III's and have the chip re-calibrated for them.

If not then yeah, there's another issue going on some place.

 

My thoughts were headed towards an issue with the wiring going to the IAC motor. That, or the passage in the throttle body is plugged.

 

Anybody know how to post vid on this forum?

 

I checked the passage. Took out the IAC Valve and blasted Carb Cleaner through it, was clean as could be. I turned up the set screw again to idle at 1K but the idle hunts back down to 800, then will die. I took a video of it but don't have a YouTube account to post the link to. Was hoping to be able to post it on the forum. Oh well.

When it does hold idle while in gear, I can turn the steering wheel and it will cause the RPMs to drop and die. Has something to do with engine load at idle, vacuum. With the brake booster disconnected there is no issue at all.

Could the O2 sensor cause something like this? It's definitely an AFR or vacuum issue. What about the Manifold Air Temp Sensor (commonly referred to as the IAT sensor) in the plenum. When I had it off I sprayed a bunch of carb cleaner in it to clean off all the oil residue. I'm not sure what role the IAT sensor plays with idle on these cars.

 

Sounds like the brake booster has a vacuum leak...

RBob.

 

I agree with RBob. Do check for a vacuum leak, as they are most noticeable at idle/ just off idle. Also, pull the plugs and see what they are like.

 

If so, can wait an hour or so after shutting off the engine, then pull the check valve out and see if you get a "wooosh" sound of air rushing through the hole.

 

If you have a hand held vacuum pump and an ohmmeter you can test it.

 

I had a very similar stalling when putting in gear issue a couple years ago. Turned out to be the Ignition Control Module. Old one looked fine but was bad. Would idle fine and would stay running in gear at higher rpm but at idle would stall about 80% of the time.

 

I don't see anywhere that you have performed the minimum idle air setting procedure.....

GD

 

I will have to try it again. Since the TPS is a non adjustable one I noticed that the vdc was originally like 5.6. For ***** and giggle I tapped out the protective cap and adjusted the set screw until it was 5.4. The car was working perfectly so I'm not sure why I would have to set the minimum idle setting but will go through it again. But I will try anything at this point. I just had my son fill up the car and he said it drives great unless you are in park and then drop it into drive..then it dies unless your foot is off the brake and you just let it go.

I have tried to follow this procedure. But the car will not idle at all without the IACV hooked up or me stepping on the gas significantly. Here is the link
https://www.thirdgen.org/forums/atta...w-tps-iac.html


Throttle Stop Screw (minimum air setting)

The throttle stop screw’s primary function is to prevent the throttle blade from closing too far and getting wedged/stuck in the throttle bore. However, it serves as a secondary function to adjust the minimum air setting. The “minimum air setting” is what is used to describe the amount of air that is allowed to enter the engine thru a “closed” throttle. Because the throttle valve cannot be allowed to completely close (because this would result in it getting wedged/stuck closed in the throttle bore), some air will always be allowed to enter the engine around the throttle valve.



On a 100% factory stock engine, you should never need to adjust the throttle stop screw. This is the reason why GM installs a tamper-proof plug over the throttle stop screw on the throttle body. But there are times when the adjustment of this screw is necessary. One example of this is when the engine is modified, or a different throttle body is being used than what originally came with the engine.



Larger displacement engines require more air to maintain a set idle speed. Aftermarket camshafts with lots of duration or lots of overlap tend to lower the amount of vacuum an engine can generate at idle. Lower vacuum levels translate to less pressure differential between the intake manifold and outside (ambient) air. This means there isn’t as much pressure difference to force air into the engine around the throttle blade or thru the IAC passage at idle. And either the IAC needs to open up or the throttle blade must be opened more to allow more air to enter the engine. Engines that have higher compression or are new/rebuilt can have higher internal loads/friction which can also result in a drop of idle vacuum levels. Basically any condition that increases load on the engine will result in the vacuum level to drop at idle, which will require the IAC or throttle blade to be opened up to compensate.



Setting the throttle stop screw can be accomplished a couple of different ways. If you have a scan tool, I recommend allowing the engine to warm up to operating temperature and then adjust the throttle stop screw in or out until the observed IAC position counts come to rest within the spec range I provided earlier. After adjusting the throttle stop screw, it may be necessary to adjust the Throttle Position Sensor, which we discussed in my Jan/Feb 2008 segment. On cars that don’t have an adjustable throttle position sensor, the ECM automatically learns the “closed throttle” voltage when the ignition is keyed on (after the key has been off for at least 10 seconds). If you don’t have a scan tool and you are working with a pre 1994 model year ECM, you should be able to adjust the minimum air setting by doing the following steps…



1) With the IAC valve connected, ground the diagnostic (ALDL) terminal (same as you would do to flash trouble codes thru the check engine light).

2) Turn ON the ignition, but do NOT start the engine. Wait at least 30 seconds.

3) With the ignition still on, disconnect the IAC electrical connector.

4) Remove grounding of the diagnostic (ALDL) connector and start the engine. Allow the engine to fully warm up and go into closed loop.

5) Adjust the idle stop screw so the engine idle speed obtains 550rpm in drive (auto trans) or 650rpm in neutral (manual trans).

6) Turn the ignition off. Disconnect power from the ECM for at least 10 seconds to clear codes (in case any are present) and reconnect the IAC electrical connector.

 

I believe I have narrowed this down to possibly the brakes. I swapped out the EGR valve and installed an adjustable FPR but that didn't fix the issue with the stall. The car actually runs excellent other than this issue. The issue is only happening after I have been driving for awhile and haven't really applied the brakes, then when I come to a stop (at a signal) with my foot on the brake pedal for a few seconds the idle will gradually drop and then die. I had somebody sit in the car and depress the brake pedal and release every few seconds and noticed the idle going up and down. As I had the hood open I noticed that there was air bubbling in the rear part of the master cylinder.

When this issue first started with the car, it happened after I had the brakes on and the driver's side brake cylinder (drum) popped the seal and lost brake pressure, I got the light on the dash for "Brake" as the proportioning valve shifted due to a loss of brake pressure.

I replaced the rear drum brake cylinder and bled that side only. There must be air still in the system for the master cylinder to be bubbling. So I will re-blead the brakes and see if that fixes the issue. I'm assuming with the air not compressing in the brake system that when I depress the brakes it is causing some fluctuation in the vacuum as the brake booster changes due to fluid pressure changes in the brake lines and master cylinder. I check the brake booster check valve and vacuum and it is good.

 

Well that wasn't it. I will have to go back to the drawing board to figure out why I am not able to set the minimum air idle settings as described above. Whenever I disconnect the IACV the vehicle will not start, it must close off when I unplug it. Per the instructions it's supposed to run so that the minimum air can be set at 550 rpms.

 

Wow forgot some basic stuff and it cost me a few $$ to figure out. I installed a new distributor today because there was a guy on Youtube who was having the same issue as mine, the car runs great then if you throw it in reverse and turn the wheel or place any load the rpms fall and the engine stalls/dies. He ended up thinking it was a ignition timing issue and after replacing the IACV, TPS, and others it didn't resolve the issue. He ended up replacing the dizzy and it solved the issue. So I noticed the alternator on my car was original and I already replaced the cap, rotor, and ICM. Originally it was randomly dieing because the ignition coil was shorting out.

After I replaced the dizzy, I was resetting the base timing 6* btdc after the car warmed up and noticed the alternator was kind of making noise, I put a digital MM on the posts and it had good output, like 14vdc. But before I road tested I decided to go ahead an disconnect the amp powering my two 12" subs from the battery. I took the car for spin and the issue is gone. It no longer dies at a stop or when there is a load like the AC compressor kicking on, turning the steering wheel, stepping on the brake, and or selecting Drive or Reverse. I was guaranteed that if I did that previously it would die. Even though it didn't die this time I still heard what sounded like the alternator straining each time I turned the steering wheel or the AC compressor kicked on...so load on the engine.

I plan on hooking up the amp wire back to the battery to try and replicate the stalling problem. But I'm thinking that a new high output alternator is what is needed to keep the volts up to all of the systems when the engine is under some sort of load.

 

Just want to close the loop on anybody who might be doing a search that the issue I was having was solely related to the alternator and use of an aftermarket amp to drive the 2 12" subs I have in the rear. The OEM alternator did not have enough juice at idle to provide the necessary voltage to the rest of the electrical system to keep idling while under load.

I have also ordered new positive and negative HD wiring from Gary at innovative wiring. According to others that have upgraded the positive and negative leads this has made a noticeable difference.
http://innovativewiring.com/?page_id=182

 

Thank you for posting your results. Many times these threads seem to just go away with no resolution. Your information could be very helpful to someone fighting this same kind of problem in the future.

 

Thanks Vader. Too ofter I have done searches on this forum and others and so much advice is given and then there isn't a response as to whether or not the issue was resolved. I often wonder if this is why I see so many Thirdgens sitting in fields or outside next to somebody's garage. Thirdgens have such a classic cool look now. I drive it regularly and every time I'm out on the road I get thumbs up....and they are multi-cultural thumbs up. They are either guys that look like Joe Dirt, Run DMC, or Cheech and Chong....jk'ing. Some kid (early 20 something) servicing (means using a tablet) my Tesla at my house saw my C8 and asked to take pics, almost immediately after he saw my Thirdgen and spent just as much time checking it out. It is pretty cool how much attention a clean running Thirdgen draws.

 

Thanks Shinobi'sZ for the detailed description of the issue and all the steps you've done to cure it. Unfortunately, my 1990 Camaro RS does the exact thing - dies only at stops when I have my foot on brakes. Start-up/ driving is great, I have no issues in acceleration etc. I replaced the EGR valve, IAC, spark plugs and am about to replace fuel pressure regulator (FPR). I am having now second thoughts on FPR being the culprit based on your description and other write ups.
So, the alternator ended up being the main issue for you? Or you think the alternator and dizzy both contributed the issue? What brand alternator did you install?
I don't have subs in the car. Thanks much

 

In my case after chasing everything down pretty much piece by piece to isolate the issue. It ended up being the alternator. Check your grounds too, I purchased the heavy duty ground harness but haven't had to install it yet. During the summer when it was 115* outside I used the car during the day and night with the headlights, AC, turn signal, and stereo on, selecting gears from P to D to R back to D and no issues. Was for sure my alternator. I just have new sensors and parts for everything else now too. lol.

 

I realize this is a very old post, but I'm having the same issue with an '89 Firebird. Wtf is a Dizzy?

 

Hot rodder slang for distributor.

 

Really? I've never heard that one. Only time I've ever heard that was when they were talking about someone's girlfriend haha.
Thanks!