1988 cutlass ciera idle surge
 

Hi, I was wondering if anyone had any addt'l things to check. I have an '88 cutlass ciera with the 3.8L. I've owned car for 8 months. 130k miles, runs real good. The prior owner had the head gaskets replaced approx 14k miles ago. Ever since I owned the car, the temp gauge never got above about 160. About 4 or 5 times since I've had the car I would get an intermittent idle surge, whether in Park or in Drive. It was bad enough to stall the engine a couple times however when I would restart the car, the idle would be fine.

I got around to changing the thermostat this weekend to the factory 195 stat. It had a 162 stat in it. Now I have a constant idle surge in Park or in Gear. I also installed new AC delco R44lts spark plugs. I have sprayed brake clean all over the engine looking for vac. leaks, checked pcv valve, replaced IAC valve, cleaned the inner part of the bore when IAC was removed, MAF was replaced just prior to me buying car. All vac. lines look good. Fuel pressure is 31 at idle in Park and 40 with the vac. line removed. Car runs great down the road, has plenty of power. I have tapped on the MAF while engine is running and no change in idle surge. I have tried to ohm CTS but only get OL. I have unplugged CTS while engine is in closed loop and get a CTS code and idle changes so I assume it is working. Is this correct?

On occassion I get a code 32 for EGR. I have checked all components. I have even disconnected vac. line to EGR valve and solenoid and plugged all lines and I still have the same idle surge.

I noticed the idle surge seems to get bad as engine warms up. When cold it runs better at idle.

What else can I check or should I do? Air filter and fuel filter are new. The plugs I removed looked good. I don't understand why I have a constant idle surge now from just changing plugs and installing stat. I plan to ohm the injectors and run some injector cleaner through the tank tomorrow night.

I'm leaning towards an intake gasket vac. leak but am surprised I couldn't detect it when spraying it. I really don't want to put the time into the intake change before checking other simpler things.

Any input would be appreciated. Sorry this is so long. Thanks.

I found a lot of my problems was the throttle positioning sensor don't know if this would work for you but your crank sensor also will cause a bad idle it feels like a loping idle that's getting ready to stall at any minute my car did the same thing my engine is a 4.0 L though with the same problem I changed coil packs spark plugs went through everything and the throttle positioning sensor the last thing I replaced fixed it I also replaced the map sensor at the same time so it could been one of the two or both