Odd... Car runs great warm, but not cold
 

My 88 has an issue with running cold. It is odd, I can find 1000's of threads about issues where it runs cold and shuts off warm or won't re-start warm, but not the opposite. This issue I have is, when I first start the car, it will idle up around 1K RPMs and after 15-20 seconds or so it will start to stumble and die if I don't feather the throttle a bit... then it comes right back up, and will idle for a while and then... start trying to die again and will if I don't feather the throttle again.

After a few minutes of this, if I try to drive it out of the garage, it struggles horribly. Almost like the TPS is reading right. If you open the throttle it won't do anything to try and accelerate the car. Just lugs around, but actually doesn't die. Put it back in neutral, and then you can rev it up, but put it back in D and it goes right bag to lugging around. After a few laps around the neighborhood, it then will run normally and I can go out and drive.

It has a re-man ECU
I had replaced the MAF relays and MAF to get rid of the code 36 I was getting (Now has Bosch)
New IAC in the last year (about 500 miles) and minimum idle reset procedure performed. When warm it idles in P between 500-600RPMS and about 800 or so in P.
Code 34 previously corrected as well... had part of the supercharger piping break - has been repaired.
Previously had a gas leak from the O-Ring to the 9th injector.

It did sit over the winter and does have old gas. It has Stabil in it, but the gas may have been 3 or 4 weeks old when I treated it. It wasn't the plan, just some other things got in the way and I had it up on jack stands for a brake overhaul as well. I did put about a half tanks of fresh 93 in it last night.

I know I need to get some data logs, but while I am logging what should I be looking into?

Car has a supercharger kit with an MSD 6AL as well as an MSD boost retard box, headers with no AIR and about 62K miles.

Re: Odd... Car runs great warm, but not cold
 

Since I never let anything go, I guess I can't tell you to search for threads with symptoms of failing injectors. :2cents:

Re: Odd... Car runs great warm, but not cold
 

Things to check - Coolant temp sensor reading off 20+ degrees cold. MAF is the only fuel control cold until the O2 sensor becomes active and fine tunes fuel trims. Check for debris in front of MAF like from a mouse or insects.

Re: Odd... Car runs great warm, but not cold
 

Oh, I should add I did replace the O2 last summer as well. Has a Bosch unit.

Doesn't seem to have issues when it is warm. I will check round the MAF, but shouldn't have anything in the way. It seems to suck air in just fine once out driving, but it only takes a minute to look. I will see what the ECM reads from the CTS at start up.

Re: Odd... Car runs great warm, but not cold
 

All it takes is there to be something in front of the MAF that disrupts the airflow which skews the reading. I don't think something is blocking the airflow. If you have a scanner, what are the fuel trims?

Re: Odd... Car runs great warm, but not cold
 

I have WinALDL and a MOATES cable.

My only concern there is there may not be enough miles logged since the last time the battery was unplugged to get a full picture. I plan on cleaning on her tonight and doing some scans. The good news is it is very reliable that is has issues for the first few minutes before driving. So, I should be able to get some comparison logs.

Going to also get some fuel pressure readings.

Re: Odd... Car runs great warm, but not cold
 

Did some diagnostics:

CTS was showing appropriate readings. When I started it was showing 107° and warmed up as I let the car run. I had driving it earlier in the morning so I feel this is appropriate even if not 100% spot on. The intake and all was still warm to the touch.

TPS Volts was .53V at idle and 4.63V at WOT (Using pedal and WinALDL) so this is what the ECM is actually reading.

Checked Fuel Pressure:
KOEO: 42PSI
Idle (W/Vacuum): 38PSI
Idle (W/O Vacuum): 46PSI

Leak Down
0 min: 42PSI
5min: 34PSI
10min: 25PSI
15min: 22PSI
20min: 19PSI
25min: 18PSI
30min: 16PSI

Also, I observed only a few cells of 8 or 12 knock counts from starting up.

I noticed the IAC was sitting at 160 and staying solid while it was struggling. So I gave the minimum throttle screw two turns out and then a half a turn back. When Idling around 1000RPMs the IAC is now in single digits.

I will need to re-adjust the TPS. It is now sitting at .69V at idle. I don't think this is much to be concerned about, but no reason not to get it set right.


Any ideas what I should be digging into next?

I didn't take the MAF piping apart yet.

Re: Odd... Car runs great warm, but not cold
 

MAF, O2, and Fuel Trims are the main readings I would be looking at with your concern. Does the car run better as soon as it switched to closed loop?

Re: Odd... Car runs great warm, but not cold
 

Yes, it absolutely does.

I can look at those in more detail and report back.

The 02 Voltage was there and cross counting. O2 sensor is a fairly new Bosch unit.

Re: Odd... Car runs great warm, but not cold
 

If it runs better as soon as it switches to closed loop shows you that your MAF readings may be off.

Re: Odd... Car runs great warm, but not cold
 

Next time I am in the garage, I will get some MAF readings.

Re: Odd... Car runs great warm, but not cold
 

Also try running with it unplugged and see if it acts any different.

Re: Odd... Car runs great warm, but not cold
 

Didn't get a lot of time to spend with the IROC last night. It did act a bit different, possibly because it was in ALDL mode.


Here is a video:

Re: Odd... Car runs great warm, but not cold
 

New development. I noticed while I was doing scans, Code 36 flag was still on. I hadn't reset the computer since I swapped MAFs. So, I disconnected the battery, hooked it back up, and not it will barely start. Will only stay running if I work the throttle.

And I mean work it. I have to apply throttle and let go. When opening the throttle, I can get the RPMs to come up and prevent it from stalling. However, if I leave it down (Say about 1/4 throttle and about 1.2V on the TPS, it will stall and die. If I don't do anything it will stall and die, but if I work the throttle in and out all is well. https://www.corvetteforum.com/forums...ilies/mad5.gif

Re: Odd... Car runs great warm, but not cold
 

Disconnecting the battery may have erased your fuel trims. I assume the car is running very rich or very lean. Finding out which one will help decide how you go about testing and what you can look for. Did you try to disconnect the MAF connector again?

Re: Odd... Car runs great warm, but not cold
 

Yea, that is what I was telling my wife. What ever the computer had "learned" to deal with the issue got erased.

It smells rich, but it doesn't have a catalytic converter... and obviously it is struggling to run so it's probably not getting a complete burn. Now, the car has a O2 gage reading the narrow band sensor. It tends to stay to the lean side. Obviously it has the fuel pressure it needs to idle, so I don't think it is a lack of fuel supply or the ability of the ECM to open a large enough pulse width to feed to fuel. Though, I say it seems lean, but the IAC is trying to open up to bring up the RPM and opening the throttle helps. This would seem to point to being rich and into the circular flow we go.

With that circular sentence written, I am starting to wonder if the hunt for air and fuel isn't because of the ignition :confused:

Cause here we go again.... So I saw knock counts last night. High ones when it was trying to idle. Are the knock counts real because of being lean or is it pulling some much timing it won't run? No timing, incomplete burn, shows rich, pulls fuel... sees lean... dumps fuel in, chokes, opens IAC, then goes lean, knocks, pulls timing... and so on.

Knock sensors are pretty cheap and as much as I hate the throw parts at a car to solve issues, a $25 sensor to eliminate it would't hurt the wallet too much. Haven't found a way to test it.


The BLMs build. It is acting as if it is seeing lean.

I have not. This MAF is new to the situation. When I bought it, it had a Spectre Thin hot film style MAF on it that was causing a Code 36 to stay on. This one is the Hot Wire Bosch Style... solved the Code 36. MAF readings (from what I have found by reading around) look appropriate. Go up/Down with RPM and show values similar to what I have found in posts here. It has struggled with Idle with both MAFs and Two different ECMs.

I picked up an ECM last year when I got the car to have the ability to swap them out for diagnostics and also in case I got to burning my own chips or go EBL or whatever. Though, that is long term plans and I won't be doing any more engine mods until I can solve this idle problem.

Re: Odd... Car runs great warm, but not cold
 

If you have enough to go on thinking the car is running rich but O2 is suck lean, maybe you have an O2 sensor problem. You can't use many of the readings like IAC when the car isn't stable. Your "new" maf is probably just a refurbished unit which are not very dependable out of the box. Knock sensor probably isn't the route I would go to fix this issue.

Re: Odd... Car runs great warm, but not cold
 

Yes, obviously it is a re manufactured unit. I don't believe new is even available anymore. 02 Was replaced as well. TBH, You could consider the MAF has been swapped and corrected Code 36, ECM has been swapped, and so has the IAC.

IAC was because I didn't like how the Pentil and spring looked after cleaning.
The 02 as general maintenance
The ECM because I could and have a spare.
MAF was to get rid of the CEL for Code 36

Mainly all last summer.

But all was in the process of trying to find the root of the issue
Timing was checked
IAC reset procedure was done
IAC housing has been cleaned
PCV line that was disconnected has been taken care of
MAF Relays were checked as well.


Now it is worse. Before disconnecting the ECM... at least it would warm up and then run well. Now it won't stay running long enough to get warm LOL.



I took a break from working on this issue and went ahead and did the brakes

My Wife keeps telling me I wanted I project. :blah:

Re: Odd... Car runs great warm, but not cold
 

So, finally had a few evenings to play around with things. Just for S&G's I unplugged the MAF, started the car and it idled. So, I spent some time swapping between the new style MAF that was on the car and the old style I ordered from Advance Auto. Well, it runs with the old MAF but my code 36 comes right back.

No codes with the old style MAF, but it wouldn't idle until warm. Very strange, but it is what it is. BLMs around 126 and the IAC is sub 20 counts holding idle. :thumbsup:

Code 36 keeping SES light on :gocrazy:

I guess I am going to bite the bullet soon and buy the stuff to burn chips so I can turn it off and a few other things.

Now onto other aspects.

Re: Odd... Car runs great warm, but not cold
 

Have no basis for this but the thought occurred so I'm throwing this out there. The MAF works by heating up the wire, it could be that you are not getting enough current at the MAF or not enough ground to properly heat the wire on the new style MAF, and the old style is tripping the code for the same reason?

Re: Odd... Car runs great warm, but not cold
 

Old style (OEM Type Bosch unit) - new to me.... No codes. Didn't want to run but no 33,34 or 36. So the burn off cycle worked, or I should say at least the ECM get's the confirmation voltage to return.

New Style (Thin Film) - was on the car when I got it.... Code 36 but runs.

I would have expected if the MAF was causing the issue, some code would have been flagged by the ECM.

Don't get me wrong, it doesn't run perfect. I have some logging to do. The car has no AIR, a Supercharger, Headers and other things. Still has a bit of stumble at tip in off idle. Personally, I think I the tune may need some adjustments. With the supercharger kit, it may need a bump in requested RPM to idle at once warm and in closed loop.

Just going to keep plugin away, verifying things as I study tuning and get all the hardware so I can make some adjustments.

Re: Odd... Car runs great warm, but not cold
 

Ahh didn't see the supercharger and other mods... I would agree need to get the tune right. Are you running larger injectors?

Re: Odd... Car runs great warm, but not cold
 

It's an old school kit. 6PSI, uses a FMU and booster pump with an MSD Boost Retard box. No additional tuning or injector changes needed.

Not to say that a proper sized in-tank pump, larger injectors, and custom tuning wouldn't yield more power... but like the TPI it's it's old technology.

I believe I have BoschIII 22lb replacements. I didn't put them in and am only identifying by visual. I would say I am 90% sure that is what they are.

Everyone thinks a supercharger or turbo changes everything, but as far as idle and light throttle, the bypass valve is fully opened and the engine is only sucking in what it needs. There is no variation in vacuum at idle from factory and the supercharger itself isn't compressing air so it's not putting much of an additional load on the engine. This is the same for cruising operation and light throttle. Until the vacuum drops enough to allow the bypass valve to close. However, I believe another 50-100 RPMs may help the idle. Just like with a bigger cam, sometimes the engine just needs to be sped up a bit to smooth out.

Just setting it with the throttle stop screw may not be enough. Have get the IAC in range so it can do it's thing and actually control it

Re: Odd... Car runs great warm, but not cold
 

Kyle,
You might want to consider the EBL system the Flash one is $475 including the ECM and you can delete your MAF sensor.
http://www.dynamicefi.com/EBL_Flash.php
The P4 system I have has some advantages but the wiring is much more complex to do the conversion.
You still use tuner pro to modify the BIN but you no longer have to burn chips.
A big plus over using the Flash vs the P4 system is the mount for the ECM is different I had to mod the RH front speaker mount to make room for the 90-92 '730 ECM mount as the wires that plug in are in 3 not 2 connectors.
It's self tuning just like a number of the other systems around. Hope to have my car up and running in a couple of weeks if you want to wait and see the P4 system in action...
Dave

Re: Odd... Car runs great warm, but not cold
 

Yup, Looking forward to yours being up and running. I may go that route eventually. My Dad's RV is in my driveway, so both of the Hot Rods will be dormant for a few weeks.


It's hard to tell. I need to get some data logging in and see what some data tells me. With the supercharger, it may simplify any tuning tweaks I need by keeping the MAF. That statement being based on a overview level difference of MAP/MAF. The devil is in the details and once yours is running we can take a harder look at how it may work for me. Right now I think I am a bit lean in the higher RPMs, but I need to verify with something other than the narrow band O2. Depending on how that shakes out, I will have to consider the cost associated with the remedies and long term benefits.

I really want to get a stereo in it before I make any other performance modifications. I may leave some performance on the table in the near term to get some other things done.