Low Idle Very Rough

1988 ciera 2.8 154000 miles.
Car started to idle rough, not to bad seemed sporadic. I changed plugs. No change in idle. It did have more spunk. Took car to Auto Zone and they hooked there Diag. to it. Error MSG were 21, 13, 23, 33, 34, 54,61,63. Changed the O2 Sensor and the TPS. In order to get to the TPS I had to remove a sensor, I think? It is sitting on top of the TPS and plugs in to the throttle body also has 4 wires to it. I took this unit off Two screws only and it has a spring and a small shaft. I forget what they called it. (low idle adjuster or?) That unit looked pretty beat up. Black inside and seemed loose. I probably screwed it up. Anyway . when i got it back in I reset the computer, unplugged the neg term for 30 seconds. and started the car. It runs very rough at idle, or coasting at any speed or on deaccelerating. When I give it gas runs excellent and very strong. Got back to hook up diag. again. Error msr. was 14. They said something w/ O2 sensor, Unplugged or something else is effecting it. I think it has something to do with the unit that Sits above the TPs/ Please help. Thank you

The thing you removed was probably the idle air controller. You may need a new one to smooth the idle out. Based on your description, I would remove the throttle body and clean it good with throttle body cleaner. Replace the IAC and your idle problem should go away. Remember to allow the computer to relearn the idle by using the case learn procedure spelled out in your manual. A good throttle body cleaning, while you are at it won't hurt either.

The thing you removed was probably the idle air controller. You may need a new one to smooth the idle out. Based on your description, I would remove the throttle body and clean it good with throttle body cleaner. Replace the IAC and your idle problem should go away. Remember to allow the computer to relearn the idle by using the case learn procedure spelled out in your manual. A good throttle body cleaning, while you are at it won't hurt either.


Thank you very much. I will clean it tomorrow. Part of my problem is I do not have a manual. I am helping a friend. You said case learn procedure! I guess I will get a manual to see how to do that. I also noticed that on acceleration I have a lot of white smoke where I never had that before. She runs great on acceleration. Anyway, I will replace that unit. It is 39.00 at auto zone. Thanks again.

Where is the white smoke coming from? Do you have any water in the oil? If there is water in the oil you may have a bad intake manifold gasket. If it is coming out the tailpipe you may have a bad head gasket. Water in the oil will cause rough idleing and do major damage if not taken car of. I had a highmileage 2.8 and the intake manifold gasket went bad. I noticed it because the idle was rough due to the water sending steam back through the the throttle body. So check to make sure that is not causing part of your problem. Gasket is not hard to change but will take several hours.

Looked at oil from dip stick and seems free of water. Looked again and I think I have a leak in the muffler(Iknow). But it does seem to have not really I white smoke or dark, just light brown.. I thought it would be because car is running rich. I think it is getting 10 miles to the gallon. I will replace the Maf also. Is that a good Idea?. Thank you for your help.

Replacing the MAF sensor is not a bad idea as it will help the idle issue. It may however just be dirty and a can of electronics cleaner is cheaper than a sensor. When you clean it just be very careful to spray it lightly and allow to completely dry before you put it back in.

I will get to this today. Your help has been a god send and much appreciated. I will let you know how I make out.Thank you

I will get to this today. Your help has been a god send and much appreciated. I will let you know how I make out. Thank you
OK, I finally got Back to the Oldsmobile. I replaced the IAC . And cleaned the MAF. First I cleaned the MAF to see if that was the answer. It was not, So Put new IAC in and a Significant difference. car Idled great. Did the 40 miles an hour down the road for a few miles to train it. It ran great . After a few miles it was running a bit rough not bad but enough to bother you. Also noticed A darker smoke . I wonder if I hurt the new O2 sensor with the car car running so rich. I should also replace the MAF. This stuff sure adds up! You think this is the Avenue I should go!. Your input has been very Valuable to me ,,Thanks

Don't worry about the MAF yet. Replace the O2 sensor with a new one. It is probably sending an incorrect signal to the computer causing it to put more fuel into the engine than needed thus the black smoke.

Don't worry about the MAF yet. Replace the O2 sensor with a new one. It is probably sending an incorrect signal to the computer causing it to put more fuel into the engine than needed thus the black smoke.
I am Getting a new one (O2 sensor)today. I replaced the O2 sensor when I replaced the plugs. a week ago. The manual said that if the car was running rich it could damage the O2 sensor. I will let you know the outcome. Thanks again for the fast responses.

I am Getting a new one (O2 sensor)today. I replaced the O2 sensor when I replaced the plugs. a week ago. The manual said that if the car was running rich it could damage the O2 sensor. I will let you know the outcome. Thanks again for the fast responses.


OK, I put new O2 sensor in, Also I put new PVC valve in. That PCV was seriously plugged with crap(oil ) thick. I need to take the hose off and clean it out. looks like a chore to get the hose off. The week old O2 sensor was loaded with carbon very black and thick. Anyway, Put these Items on and reset computer. started car and still is rough , not as bad, but does not idle even. Does not stall, just a bit rough. I will take for a drive. The dealer set to train the IAC ,I will need to have scanned. Is there any other way to train the IAC. They also said to replace injectors. Should I take on this Task?I wanted to tell you that when the car was running I unplugged the MAF, and the rpm went way up. I think that would tell me that the MAF is functioning!. Talk with you soon, Thanks

OK, I put new O2 sensor in, Also I put new PVC valve in. That PCV was seriously plugged with crap(oil ) thick. I need to take the hose off and clean it out. looks like a chore to get the hose off. The week old O2 sensor was loaded with carbon very black and thick. Anyway, Put these Items on and reset computer. started car and still is rough , not as bad, but does not idle even. Does not stall, just a bit rough. I will take for a drive. The dealer set to train the IAC ,I will need to have scanned. Is there any other way to train the IAC. They also said to replace injectors. Should I take on this Task?I wanted to tell you that when the car was running I unplugged the MAF, and the rpm went way up. I think that would tell me that the MAF is functioning!. Talk with you soon, Thanks

I read in a search that to train the TPC put chalks in front of the tires start car Put it in drive apply parking brake, and let the car idle for 30 minutes. When that is done turn car off and let cool, and do the same thing for ten minutes. Anyone hears of that, I will try anyway. This car is blowng some serious dark smoke, I thnk I should tackle theEGR and clean it

[QUOTE=jondaboll]I read in a search that to train the TPC put chalks in front of the tires start car Put it in drive apply parking brake, and let the car idle for 30 minutes. When that is done turn car off and let cool, and do the same thing for ten minutes. Anyone hears of that, I will try anyway. This car is blowng some serious dark smoke, I thnk I should tackle theEGR and clean it[/QUOTE

YES! THE CAR RUNS BETTER THAN IT DID 15 YEARS AGO(Almost)The solution was a combo of things. Most of all I think it was cleaning the throttle body and EGR valve. Throttle bdy and the EGR was like black tar. I ran the car all day and it seems as if the TPS has trained itself also. So to wrap this up we,Changed plugs, O2 sensor, TPS, IAC, AIr filter, PCV, Cleaned throttle body and EGR(Made sure the diaphram in the EGR was moving freely) cleaned passages from egr to throttle body . Cleaned MAF with electronics spray and very carefully. Thats it! She runs great. Thank you so much GTP DAD.....

Always brings a smile to my face when someone gets their car back in working order. Good Luck!