my car had been running fine when I parked it. Occasionally I'd start it up to move it and everything was fine. Then one time I couldn't get it to start. I discovered that if I give it some throttle (like you'd start a carb'd car), it would start. It won't idle on it's own... I have to give it gas to keep it idling. It smells extremely rich, and my scan tool indicates that it is indeed rich. O2 voltage stays real high, and cometimes it'll throw a "o2 sensor rich" code.

I backed off on my fuel pressure with no improvement. Temp sensors all seem to be functioning properly. Fuel pressure seems to be proper. Where do I look next?

 

You've done all the things I would have done to confirm a rich conditon. Now you only need to find the source. Typical suspects are FPR leakage and injector leakage. The other less common possibilities are incomplete combustion, or a stuck EVAP purge valve. There is also a slight possibility that the cold start valve is leaking or remaining ON.

Does fuel pressure remain after the engine is shut off? If so, that would tend to indicate that the injectors, FPR, and cold start are not mechanically stuck or leaking through.

The FPR is easy to check by pulling the pilot vacuum hose.

The EVAP would be fairly easy to check by simply disconnecting the purge line and plugging it.

The cold start injector/valve may be a little more tricky to diagnose. You can remove the electrical connector to make sure it isn't being powered, but you may have more difficulty determining if it is leaking through.

Injectors may be a little more involved, since a power balance test will probably be necessary to identify any offenders. My guess is that it's in the left side, or the O² wouldn't be picking it up.

Keep us posted, please.
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Oh - Never mind the "Cold Start" comments. I just realized that this was for a '91, and NOT your '85.

Since it is a S/D TPI, you might also want to verify the MAP signal and IAT temperature reading with the scanner.

 

Fuel pressure holds after I shut the car off, at least as long as I have patience to wait, which is a couple minutes. If it was leaking bad enough to cause a rich condition, I would expect pressure to leak down immediately.

IAT temp is functioning properly. I think I forgot to check MAP signal, so I'll try that. I'll also give the EVAP a try.

Thanks for the troubleshooting help. I'll post my results as soon as I get a chance to fool with it.

 

I checked my MAP voltage. It's hovering around 1.75 volts at idle and jumps to 2.5-3 volts when I blip the throttle.

I need to check the canister purge... as soon as I can find the cannister. It's not anywhere under the hood like it is on a thirdgen. Once I find it, how do I test it?

 

Jim, how are you doing? I have a guess: a non-functioning IAC.

 

Hi Doc,
I had thought about the IAC too. Although it won't fix my rich condition, it may be related to my failure to idle. I think I've got a spare one hanging around, so I'll try swapping that out.

 

Update.

The other day I finally had time to screw with the purge cannister. I took it out and inspected it, and it seemed fine. I removed the vacuum line going to the throttle body and plugged it. The car seemed to idle better to the extent that it would ALMOST idle on it's own instead of dieing immediately. Obviously this didn't fix the problem, but it seemed to impact it. I took the car for a ride last night, hoping that using it may help change something, or at least expose the problem. I never noticed a rich unburnt fuel smell, and the service engine light didn't come on. The car drove ok other than a bit of a throttle tip-in problem and the obvious problem of the RPMs diving and wanting to stall when throwing in the clutch. After about a 5 mile ride, the car idled no differently.

Next time I get a minute I'm going to try swapping the IAC to see if that makes a difference. If that doesn't work, I don't know what the hell do try next.

 

Swapping the IAC didn't help. I'm officially out of ideas.

 

Check the temp sensor in the intake manifold.I was driving my truck one day and it was running fine then it just quit .I barely got it home I had a spare motor so I changed all the sensors on my truck so I thought still wouldnt run. A friend cam over with a scan tool ,it said the truck was running at 30 below zero changed the temp sensor and it ran fine.

 

I second that. Check both temp sensor readings. I had a rich condition from a bad CTS before.

Lou

 

Looks like it was the IAC afterall. I put the car back together and started it after swapping the iac and it still stalled, but on Saturday I had to move the car out of the garage and it started and ran fine. Maybe the IAC just needed a little more time to park and start working fine. Of course I threw an "o2 rich" code because I forgot to plug the manifold temp sensor back in, but now it's all good.

Thanks for all of the help everybody.

 

hi guys, hope you dont mind me jumping on to the end of this thread but id rather do that than start another one! i have an 87 t/a with a 350 tpi from a 91 gta. ive keep the maf set up, and it ran fine, even with the 305 e-prom (which has since been replaced with a motovation custom chip). the same problam with starting happened when i changed the throttle body for a 52mm. the engine has edlebrok heads, cam, roller rockers and headers so its no stocker. i have to feather the throttle until it warms up a bit. i dont get a ses light come on until the engine dies. the saturday just gone i ran 13.6 @ 100 and 11.9 @114 with 150 shot, so it does run pretty good! any ideas as to what is causing my problam? im thinking a vacum line? and it does smell of gas.

 

If it smells of gas, I'd try disconnecting the vacuum line that goes from the purge solenoid to the throttle body. This will help you determine whether the purge solenoid is allowing gas fumes into the plenum.

I have another question too. What kind of throttle body? I put a holley 52mm throttle body on my IROC and my IAC circuit hasn't functioned since. I've had to compensate by opening the throttle blades on the TB to make it idle, but because of that my throttle response sucks. You may want to try swapping back to the stock throttle body to see if that helps.

 

when you say purge solonoid do you mean the charcoal canister? only i trashed that ages ago. i think the vacum line is still open though. and its a bbk t/b. lots of response and really livens it up in the upper rpm range.

 

The purge solenoid is what opens/closes the line between the charcoal cannister and your throttle body. If you've got an open vacuum line, that's obviously a bad thing and is something you'd want to correct.

 

Put it on a scanner. Check TPS voltage. It should read .54 volts at idle. If the motor runs like crap and is running rich, chances are the TPS sensor is either bad or sticking when the throttle blades are opening/closing. If you have an aftermarket TB, the chances are you bolted the TPS on too tight OR the arm of the TPS is rubbing the side of the throttle body. It can also stick at random. The TPS will then tell the ECM that the throttle blades are open alot more than they really are and in turn, the ECM will add EXTRA un-needed at the time fuel which will make the motor run rich and smell gassy.

This may or may not be the case for you, but I've seen it happen.
Hope this helps!