Idle searching from 6-8

[Corvette Guru]

Hello, I am new to this forum and the Corvette world . I have an 86 convertible and it runs great and plan on buying a service manual and doing some work on it myself but for now I have to settle for a mechanic ($60 an hr!). The only thing that was an issue is when starting it would turn over for about 3 seconds then the engine would start but it was a weak start. I had a mechanic look at it and he put in a new EGR valve and cleaned the TB, He said all the TPS and IAC readings where fine, But the EGR heat snsor that connects to the EGR valve pipe is bad and might be stuck open. Well after he did that the car sounds really good and runs better then ever, except it still takes 3 seconds or so to start up and now it idle searches from 6-8 only when stopped and only in the first 15 min of driving. When the car warms up it doesnt do it unless it sits running for a little while then it starts again. He claims both problems with the start up and idle could be because of the EGR heat sensor or a vacuum leak. I wanted to see what you guys think since you all know Vettes.

 

[GreenLT1]

EGR valve itself may be stuck open

The EGR temperature sensor is what the ECM uses to determine if the EGR system is working correctly. I'm guessing when you say "heat sensor stuck open" that you and/or the mechanic actually mean the EGR valve is stuck open. If that is true you will have a rough/poor idle because when the EGR valve is open, it is a vacuum leak.

 

[badglas]

EGR temp sensor

The EGR temp sensor cannot cause a hard start. This sensor is only monitored by the ECM in closed loop. It looks for an increase in temperature so that the ECM knows that the EGR valve is opening. The sensor cannot stick open. It doesn't open and close. If it doesn't work, you will have a check engine light and a code 36 stored. A vacuum leak is possible, a dirty or slow IAC motor would be more likely.

Ron Kane
Benchmark Corvette Service