Timing on a 95 silverado

[mayhem35]

Trying to adjust timing on my truck and it won't adjust. Unhooked the little brown cable set the timing to 0 with light then reconnected wire and it jumps right back up to about 1200. Can't get it to pass smog because of the high rpms.. Any advice or know how to fix problem is greatly appreciated.

 

[zora]

why are you assuming it's a timing problem. Could be throttle body related, have you checked if the vehicle has a IAC, idle air control, valve?

 

[mayhem35]

Sorry I should've put that. I replaced the IAC and checked the TPS. The only thing I haven't done is check to see if the ECM is good. I was thinking the IAC could be faulty.

 

[mayhem35]

The service engine light comes on if it sits at idle for a period of time. So I OBD-I and it comes up a 35 which is the IAC. The service light goes off after I accelerate.

 

[Chuzz]

Probably a stupid question, but have you checked for a vacuum leak? Maybe the throttle body is a touch loose. I'd check the bolts holding it in place and make sure they're tight. One just a little loose can cause a vacuum spike and be a royal pain in the neck to pin point. Check all of the screws in it too and make sure they're tight.

 

[zora]

when you replaced the IAC did you clean the passage that it fits into, usually has carbon build up. Did you check the wire harness going to the IAC for any breaks?

 

[mayhem35]

Yeah cleaned out the housing for the IAC, checked wires. Went and got another IAC last night. Gonna run a vacuum leak test and check the throttle body gasket today

 

[mayhem35]

Well, pulled the throttle body off and low and behold.....it was missing at least an inch of gasket in the front by the intake pressure line. Replaced it and the timing settled right down. Thanks for the info everyone. Much appreciated.

 

[Chuzz]

Glad to hear you got her fixed. Sometimes it's the simple things that drive us nuts, huh?