1990 Pontiac Firebird Q&A

1990 Pontiac Firebird Question: low idle

I'm putting an '89 Formula back together. The engine runs but the idle is low and jumps from 6 to 800 rpms. I tried a new maf sensor (that's the code I'm getting) but that didn't work. Spark plugs, wires, injectors are all new. I have read of others having this same problem. Could it be the EGR solenoid? Thanks for your help. -
Answer 1
The idle is conttrolled by the IAC motor (idle Air Control). The iac is a valve that adjusts airflow. What you have to do is remove the iac, clean the housing and throttle plates of carbon, then reinstall. Then you have to set the minimum aire rate. All these means is position the iac in the fully extended position, disconnect it so the ecm will not change its position, then adjust the idle to around 550 rpm's. If you had a scanner the counts should be below 20 which indicates the postion of the iac. I would start with this first. if you suspect the egr valve is not closing as it should at idle, then remove it and plug the vacuum leak created from the missing egr valve. If the idle goes to normal, suspect faulty egr or it is being commanded incorrectly from the ecm to open. -
Comment 1
Thanks. I forgot to mention that the IAC valve is new and the pintle was set at 1 & 1/18". I'll try the egr test and let you know the results. One other thing - there's a whirring noise coming from the distributer. The rotor is new and the timing is good. -
Comment 2
Do you have access to a scan tool? Knowing what the iac is doing at idle would tell us a lot. Also I would like to look at the fuel trims. Short term and Long term should be +/- 5 total. As far a s the noise in the distributor, I would remove the cap and rotor, then try to move the shaft side to side while in the car. If it moves there could be a roblem in the bearing. Also inspect the inside of the distributor cap for scraping or cantact with the rotor. -
Comment 3
I don't have a scan tool nor am I familiar with "fuel trims". I'll check the distributor as you recommended. I really appreciate your input. -
Comment 4
Well, I replaced the egr valve (figured it couldn't hurt to have a new one after 22 years), fixed a split vac house leading to back of plenum, corrected the rotor scraping inside the cap, checked all vac and electrical connections and I'm getting a fairly steady idle @ 6 to 700 rpm. My egr solenoid looks like it's pretty beat up.Could that have anything to do with the problem? -
Comment 5
So the idle is between 600-700, rpm's. I would like it to be between 750-825 at idle no load. You need to set the minimum air rate. It's like turning up the idle with the iac fully closed and disconnected. -
Comment 6
I'm pretty much of a novice mechanic. Could you explain how to do this? -
Comment 7
There should be a screw on the throttle housing, somtimes its covered by a cap. Just turn it up in 1/4 turn increments probably clockwise. -
Comment 8
That's what I thought you meant. Mission accomplished. It's running smoothly@ 850 to 900. Thanks a million for your help! -
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