Horrible Idle/Stalling, Lean Condition

Fastbull

SCCoA Member
1990 SC Has extremley rough idle and stalls after about 30 seconds if you dont give it some throttle. It has a slight miss all the way though 2k rpm then runs fine. Runs extremely strong at WOT and makes full boost and is getting around 20 vac so no vac leak. It idled fine last week then I had it apart to change the water pump and now it runs like crap. Today I checked the codes and got 41-Oxygen sensor circuit indicates system lean, right side and 91-Oxygen sensor indicates system lean, left side. Anyone have any ideas? Thanks.
 
MAF , try a PCM reset. Might be a vac leak, the vac gage can show 19-20 & still have a bad leak. If you have compressed air plug up the PVC & throttle body & pressurize the intake system. This will find any leaks. Dont go too much pressure so ya dont break the boost gage.



To do the reset via Fuse #15, you have to do the folowing;

1. Remove Fuse #15
2. Attempt to start the engine (it won't run with the fuse out)
3. Put fuse back in.

Computer is now reset.

Follow up with this INFO too

http://www.sccoa.com/articles/computerrelearn.php
 
Last edited:
ok got it to idle long enough to get 4 more codes. 72-Insufficient Mass Air Flow change during Dynamic Response Test, 73-Insufficient Throttle Position output during Dynamic Response Test, 25-Knock sensor not sensed during Dynamic Response Test, and 74-Brake on/off switch failure. Anymore ideas?
 
Those new codes are a result of missed procedures , if you have the code book it says when & how to what. You have to stab the gas & turn the wheel & pump the brakes after the "6 cyl" & the idle goes down to normal.
 
Last edited:
I tried that and got no codes guess I'll try again otherwise I guess I'm stuck with just the lean condition. Thanks.
 
Vacuum leak. Just because your gauge says 20" doesn't mean you don't have a leak. Another thing to do is clean your MAF but 95% says vacuum leak.
 
Check the line that goes between the drivers side valve cover, under the blower over to the intake tube between the MAF and the TB. Its often missed.

Fraser
 
Well I'm an idiot the lower intercooler pipe wasn't properly sealed runs like a dream now. But I am still getting code 41-lean right side, could this be an O2 sensor problem? Thanks for the replies.
 
Well I'm an idiot the lower intercooler pipe wasn't properly sealed runs like a dream now. But I am still getting code 41-lean right side, could this be an O2 sensor problem? Thanks for the replies.

Could be. If you have the ability to watch the 02 sensor voltage, look for both sides to be switching while cruising under part throttle load. If not you can swap them side to side. That will tell you if it is a sensor.
 
Ok think I'll switch the sensors but first I'm going to tear down the top end and clean it up an reseal the valve cover gaskets. It has oil running all over the place. Thanks again.
 
Back
Top