I just put on some Hedman long tube headers on and a set of Slp runners on my 91 Z-28. When I start her up she idles at about 1200 rpm after about a minute the idle starts to slowly climb and climb to about 3000. The runners are for 85 - 89. I put a Billet works 9th injector block off plate on it. I sprayed some carb cleaner on the plate it bogs down a bit but I don't think a small vacuum leak should make it idle that high. The tps was replaced about 2 years ago because it idled at 2000 all the time. I checked that out and the voltage is fine. I haven't checked the IAC yet also no engine codes are coming up. I'm running open exhaust right now and it's about minus 15 degrees celsius. If any one can help it would be greatly appreciated after all spring is coming soon.

 

The more air to the engine the higher the idle. sounds like a vacuum leak and since you just changed runners I would look it all over very carefully. if you have any scanning equipment that could show you a place to start looking.

 

I don't have any scanning equipment but I disconnected the mat sensor and and it idles at 1200 when it starts and gradually rises to over 2000 rpm after several minutes. I reconnect the mat and start it and its idling at 3000 and rising unhook it and start it up and it idles at 1200 all over again. It has thrown the code for the mat once since I finished with the headers and the intake work but hasn't even run for more than 20 min total. I'm gonna get a new mat sensor tommorow or monday and go from there.

 

Sounds just like a vacuum leak around the intake runners. Take them off slightly and re-torque down ALL of the bolts. Do them in an "even" manner. If some surfaces aren't matching up properly...try some silicone.

I'd also disconnect the battery and some sensors...and start over. No real reason other than I would want the computer to start "fresh", while knowing all of the sensors are properly connected.

 

I dont know how carb cleaner would work, but Ive always used starting fluid to spray around any new manifold when there seems to be a prob. Its worked everytime for me, the rpms will shoot up and prob solved. good luck,

 

Update figured out what the problem was and got her running. The SLP runners are for 85-88. I put the csi block off plate on and didn't even think about the egr passage on the drivers side runner being open to atmosphere. I ended up grinding the egr passage a bit to fit a dime in it and filling it with a half inch of JB weld and good to go. Thanks for all the help

 

Like the dime idea! was is possible to exchange the runners for
a '91 set? Yea, It's alittle late.. nevertheless.. way to go!