1986 back firing from the runnres or throttle body

[Rick Hendel]

I have a 1986 tpi 350 that has a rough idle for 2-3 minutes when cold. It will also back fire at the throttle body.The car runs perfect after five minutes. I checked ohms on all the injectors they were fine. I changed plugs, egr, and mas air flow senser. Any ideas? Thanks

[Duke W.]

Re: 1986 back firing from the runnres or throttle

Sounds like a lean mixture when cold. Check the PCM temp sensor - the one that senses coolant temp for the engine control electronics, not the gages, assuming they are different. Is it hard to start when cold?

Duke

[Rick Hendel]

Re: 1986 back firing from the runnres or throttle

Duke, the car starts just fine, rough idle for 2-3 minutes and will back fire if you rev the motor in netrual. Any ideas would be helpful I"m running out of money.

[Bud Landacre]

Re: 1986 back firing from the runnres or throttle

Rick,

It could also be a sticking intake valve.

[Clem Z.]

Re: 1986 back firing from the runnres or throttle

you need to check for codes in the computer. the shop manual will tell what the codes mean.

[Joe C.]

Re: 1986 back firing from the runnres or throttle

Rick:

The cold start and run characteristics on your L98 engine are determined by the output of the ECM. The ECM output, in closed loop operation, is determined by the array of inputs from the various sensors, which monitor your engine operating characteristics.

Dave Killebrew is the undisputed guru of stock TPI systems, and early C4 troubleshooting. I am not sure if he is an expert with LT1 systems as well.

Your problem is probably a dirty cold start valve (a supplemental injector, in the plenum, which enriches the mixture when the engine is cold). Get yourself a copy of the 1986 Corvette Service Manual, available from Helm Inc.

Joe