While starting the engine, there was a backfire and now the engine idles at 2000 RPM. What should I start looking at to solve this problem? Thanks for any help

Vacuum leaks would be the first thing to look for. You may have a major vacuum supply line disconnected or broken.




78 Corvette Pace Car For Sale-18k mi orig-Florida

I did find that the vacuum line had come undone from the intake manifold. I reconnected it and traced the vacuum line. Everything looked good. I disconnected the line wherever there was a fiitting and checked the vacuum The check valve seemed to work correctly. There is power to the valve, but there was no power to the Black disc shaped thing that had a 1/2" hose running to it. The air pump fuse is good. Not sure how to check the Relay. # 10 amp fuses do not have power to the
1. TRS LP
2. TRS 3/4
3. TRS 2/TCC

I have no idea what your referring to.




78 Corvette Pace Car For Sale-18k mi orig-Florida

I think the black disc thing is the air pump. when I jumped it directly to the battery it came on but did not change the RPM. I swapped out the air pump relay with the cooling fan relay and it still did not change the rpm

Why would you expect the air pump to do anything? It's just an emission control.




78 Corvette Pace Car For Sale-18k mi orig-Florida

1. TRS LP
2. TRS 3/4
3. TRS 2/TCC
I agree with Hammer. What are these readings you posted? When an engine backfires it can 'blow' off a vacuum line. The vacuum leak can and will raise engine rpm. Then, the next concern would be what caused the backfire, in the first place. If the AIR pump is dumping air during deceleration, that could cause a backfire, but wouldn't have anything to do with engine rpm. At what time did the engine backfire? While driving at a steady speed, accelerating, decelerating, engine shut-down, ect? Are you able to pull any trouble codes? (I'm assuming that the backfire and the idle speed problem started at the same time?)
Loren
SW WA

Those three "codes" are actually the fuses in the fuse box that dont have any power to them. There was a vacuum hose that blew off but that appears to be the only one and I stuck it back on. It backfired when it was being started. It seemed like it happened when my daughter released the key prematurely, and yes then when the car was started it starts idling at 3K rpm then slows down to around 2300 Rpm. I dont have a code reader, but there arent any check enginge lights illuminated

I think my next move would be to check cam timing.
Loren
SW WA

My Nephew came over. He is an apprentice mechanic at a Aston Martin dealership. He looked at it for a few minutes and found that the PCV hose had blown off. You could not see it as it was down between the firewall and the engine. He popped it back on and it now runs normal again! Thanks guys for all your advice. This problem seemed like it had so many different potential solutions. Glad it was an easy free solution this time. This is a great website.

Glad to hear it was something so simple. And, thankyou for the reply.
Loren
SW WA