90 Riv Idle Problem

My 90 Riv with 170K miles on it recently developed and idle problem. On occassion, the idle will suddenly drop causing the car to stall. It may also suddenly increase (to about 1500-2000 RPM) making it tougher to slow the car down. I suspect that it may b the idle air control valve, intake air temp sensor or ECM. I have been told that I can access the error codes through my ac unit but do not have a service manaul for this year car (have one for my old 88 Riv but had the console screen). First, any ideas on what may be the problem? Also, would error codes be logged and how do I check them to help diagnose the problem? I have the Helm service manual for a 88 Riv and assume the error codes should be the same. I just don't know how to get that info from my 90 Riv. Any input would be greatly appreciated.

Update: I went to Autozone to get my error codes checked and was told that the type of problem I was having wouldn't generate a code (check engine light never came on). I bought the control valve and will install it to see if it helps.

Questions: Is it true that codes are only generated when the check engine light comes on? How else can you troubleshoot the system?
If control valve doesn't fix it, what next? Do I try the intake temp sensor ($17) or go for a refurbished ecm ($70).


BTW, I'm still interested in knowing if I can access my codes through my ac unit.

I had a similar problem on my 90 at 240k get your mass air flow sensor cchecked it may need to be replaced. My mechanic had a problem finding out what the problem because he could not get the car to do the same thing.

I had a similar problem on my 90 at 240k get your mass air flow sensor cchecked it may need to be replaced. My mechanic had a problem finding out what the problem because he could not get the car to do the same thing.

How do uou check the mass air flow sensor? Anybody have experience with this?

My 91 riviera would also stall when I would come to a stop sign or light and slowly give it a little gas and it turned out to be a throttle positioning sensor. I am on my 3rd one.

Try tapping on it and see if the engine actsup if it doe's replace mass air flow sensor.