93 Olds Achieva, Idle Surge, Cold Misfire, Intermittent CEL

This one has me a little puzzled.

1993 Olsmobile Achieva 2.3L Quad 4.

On cold startup, car misfires for a brief amount of time. After being driven and warmed up (assuming it is a closed loop only problem), the check engine light will come on. At the time the light comes on, the cooling fan comes on also. When you let off the gas while cruising at any RPM below 2000 (assume this is the RPM limit where the PCM will take over controlling idle), the car will buck. It also idle surges when you put it into park. Then the light will go off, but the car will still do the same thing.

Car is throwin CODE 35 NO Idle Speed Control. Assumed it was the IAC and replaced it with a known good one. Still did the same thing.

I believe I may be dealing with 2 separate problems here. I am thinking the misfire on cold startup may be related to a faulty coolant temperature sensor. This may also have something to do with the cooling fan coming on. The temperature gauge reads normal when the fan comes on (I believe there are 2 separate coolant sensors for the car, one for the gauge and the other for the PCM).

What is confusing me is the intermitten CEL.

I am waiting on a friend to get me a flowchart for Code 35, and then I will work from there. Any help or insight is appreciated!

The 2.3 quad 4 is designed to turn the cooling fan on any time the check engine light is on. Code 35 indicates the IAC can not maintain desired idle. It all boils down to a vacuum leak.

Hmmm…I have checked all hoses, however I will double check again. Any common problems where these cars develop vacuum leaks?

If you had the Haynes repair manual for your 1993 Achieva, a digital voltmeter, and followed the electrical and mechanical checks of the idle air control valve, you might find out what’s wrong with it. Use a spray cleaner in the intake tract to clean the tract and the iac pintle. Use a MAF spray cleaner on the MAF sensor. A vacuum gauge is used to determine if there is a loss of vacuum.

Yes their is a common place for vacuum leaks in this model. I have attached a picture to help explain. In the photo you will notice a box labeled Oil Seperator. It is mounted above the intake manifold on the drivers side of the car. What is not shown in the picture is a 3/4 inch hose that runs from the bottom of this box to the oil fil tube. The hose runs under the intake and attaches to the oil fill tube where it enters the block. It is hard to see if you don’t know it is there. Ususally this hose rots away and begins leaking. I would check that first.

DARTMAN, thank you for that picture. I will check that today.

hellokit, I checked the Haynes. It was very vague. I did however compare the old IAC to the new one.

Resistance values of both coils were within 10ohms of the new and old one.

Ended up dropping one of the little screws holding the IAC on, so I spent all morning looking for them at the parts stores.

I did stop off at a shop and get a flowchart. Turns out the flowchart was of no use. You need the GM TECH1 scanner to do the flowchart steps. I’m going to see if I can get my hands on a Snap-on or other scanner too see what the computer is commanding to the IAC.

A Pinout chart would be handier. You could get one through alldata.com, free, if your public library has a subscription. Otherwise, alldata service is $25 per year. Use a straight pin to slide along the wire to touch the wire terminal (to avoid damaging the wire / shield), touch the straight pin with the high impedence mulitmeter positive probe to check for the voltage specified by the pinout chart. // In the Haynes Repair Manual # 38025, page 6-12, it talks of your problem and the A/C On signal. You can check the A/C comp pres sensor circuit wires, page 12-23 for grounding, or opens, between the A/C comp pres sensor and the PCM (engine computer). The gry wire is 5 volts from the PCM. The RED/BLK wire is the signal to the PCM. The BLK wire is a ground controlled by the PCM. Disconnect the car battery. Disconnect the wire connector from the PCM which has the GRY, RED/BLK, and BLK wires. Disconnect the same wires from the A/C COMP PRES SENSOR. Check the wires for opens or grounds.

Now I’m really irritated.

I found a vacuum leak from the oil separator. Fixed that and put a new intake gasket on it. No more idle surging, but still a code 35, high idle, and when put in neutral while cruising, it will rev up itself to 2000 RPM and stay there for a while. If you tap the throttle again, it will rev up higher and stay there for a while.

I did accidentally snap an ear off of the throttle body by accident, but it was not a mounting point, and I matched the gasket up to it and the intake manifold and didn’t seem to interfere with any sealing.

I’m confused now. What else could be causing this? I inspected all the vacuum lines (there aren’t many) and all are in good condition. I may try another new IAC and hope my problem was a combination of a bad IAC and a vacuum leak. I did put a scantool on it and did throttle sweep of the TPS and checked the MAP sensor, O2, and coolant temp. Any ideas are appreciated.

And you checked the A/C compressor sensor circuit wires to the PCM for grounds or opens?

I take back what I said. It is still surging.

Yes, I did check the A/C switches for open/grounds.

You checked the switch; but, did you check the wiring between the A/C pressure switch and the PCM? Did you use the MAF, and intake track, and the throttle body spray cleaners? You can cherry pick; but, it may not help you that much.

I did clean the intake ports and intake tract and throttle body.

I had it on a scanner and all sensor values were within normal range.

I am taking the throttle body off tomorrow to double check where it had broken.

Hellokit, I will check the continuity from the sensors to the PCM, however I don’t believe that is the problem, but I do appreciate your input.

If you can read the voltage values with the scan tool, you could add the “wire shake” test during the voltage check to be sure the voltage isn’t changing due to poor connection, shielding, touching, etc.