Oldsmobile 3.4L DOHC Engine Rough Idle And Stalls Out

1994 Oldsmobile Cutlass Supreme 3.4 engine. Dear BL: this car runs very good, except when at stop sign, or parked in idle, will surge, idle rough, then die, but will start right up any ideas?

See picture below. Check engine light, codes? If not, sounds like possibly a vacuum leak or the Idle Air Control valve is full of carbon. A common place for a vacuum leak is the main vacuum-T on the top of the intake near the valve body. Also vacuum leaks can occur at the EGR mounting or the adapter under the EGR valve. Try removing the IAC valve and clean it.

If the 3.4l dual overhead cam engine (position 8 of vin=X) then a VERY common area of vacuum leak is the lower intake manifold gaskets leaking. Another condition is a very high idle when cold.

Location of PVC valve and common areas of vacuum leaks on the 3.4L DOHC engine.

1- Vacuum TEE that leaks
2- IAC (idle air control) valve

Oldsmobile Cutlass Supreme 3.4L. The timing belt has shredded not broken and has jumped timing. Could this have damaged valves, what should I look for?

Yes, the DOHC engine can have the valves hit the pistons when the timing belt comes apart and jumps time. This does not happen often though.

If the engine stopped when it was running at a high speed, then that could have happened. Usually that does not happen at higher speeds, but more often just trying to start it one morning- it won't. If that is what happened, then it will normally not hit valves.

The only way to be sure is to replace the belt, time it correctly, and then do a compression test, or just try to start it.

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