1990 Riviera

I just bought this beautiful car and when I start it cold, the engine will race to 2500+ RPM's until the car is warm. Then the idle returns to normal. No trouble codes present.

I have connected a Snap-On scan tool and it shows no abnormalities. TPS voltage is normal. I replaced the IAC; no change.

I was a mechanic for 10+ years and never saw anything like this on a 3800 V6. I know this cannot be normal. I had a 92 Lumina Z34 that had the same problem and it ended up being the intake manifold gaskets.

Any help would be much appreciated. THANKS!

Rich
1990 Buick Riviera
2000 Buick Regal
1984 Chevrolet Conversion Van
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You don't need a scan tool it's all done with the AC control you will need the shop manuals, check the PCV it MUST be AC delco check the MFA and clean the thmistor.

Ok, what the problem may be is that a gasket is either old or ha some minor imperfections on it causing to do this at start up. you can use WD-40 and start at the gasket for your EGR valve. spray some WD-40 around it liberly and see if it changes the motor idle at all. If it doesn't continue on to other gaskets until you find the culprit. it will most likely be a gasket on the top part of the engine. If you get to the head gasket you have gone to far. What is happening is.... when the car is cold one of the gasket is allowing to much air in causing a mass air flow but not enough to trigger an error code. When the engine gets to temp the gasket expands thus shutting off the excess air. could even be that there might be a little warpage of metal, that can cause this happen too. if you find the gasket and replace it and it still happens, then use some 3M weatherstripping adhesive to fill in any little imperfections that there may be. this should solve your problem. Let me know how it goes.