Cascade Crew

fiveoformula · Posted: Tue Feb 03, 2009 10:14 pm Post subject: Stumped on TBI idling problem

My car runs good enough to drive everyday, If you fire it up cold, let it warm up for 5-10 minutes and drive away its fine. If you shut it off for half an hour and fire it back up, its sluggish and has to go thru the warm-up period (or so it seems).
Ocaisional stalling, slight miss, tries to idle too low sometimes, runs good when all the way warm.

Could this be an Internal issue? Or does it sound more like maybe a TPS or IAC issue? Im ruling out the tune-up stuff for now since its all new, maybe Im overthinking? Suggestions?

Boostd1 · Posted: Wed Feb 04, 2009 10:45 am Post subject:

Hey...

I would check your front 02 sensor, it could be that. I would look into replacing the 02 sensor, my car did the same thing. It would stall sometimes, it would idle all weird and a ton of other stuff. It drives fine for the first few minutes because your system is in open loop. 02 sensors have to warm up to operate correctly, hence when they are warm, your car switches to closed loop and doesn't run properly.

It probably feels sluggish because your AFR is WAY jacked up in closed loop due to a faulty 02 sensor.

Also, if you have replaced it recently, just check the connection. You may have tugged a wire during the header install or something.

fiveoformula · Posted: Wed Feb 04, 2009 9:15 pm Post subject:

That would make sense, I have replaced it recently tho... Maybe coolant temp sensor? I don't wanna just start throwing parts at it, I may put a scan tool on it tomarrow and see if I find anything wierd.

Boostd1 · Posted: Wed Feb 04, 2009 10:12 pm Post subject:

fiveoformula · Posted: Wed Feb 04, 2009 10:46 pm Post subject:

It would cause it to run wierd if the sensor is telling the computer its all the way warm when its cold tho... It could really be a million things, lol but ill check the 02.

Boostd1 · Posted: Wed Feb 04, 2009 10:53 pm Post subject:

blue89 · Posted: Thu Feb 05, 2009 8:42 am Post subject:

Might check your EGR valve. The controller on mine was haywire and would cause hard start situations when it was warm.

Boostd1 · Posted: Thu Feb 05, 2009 7:12 pm Post subject:

Twilightoptics · Posted: Thu Feb 05, 2009 7:17 pm Post subject:

If it was EGR I'd think it'd be crappy when warmed up too. Would be useful to check and make sure the EGR is sealing. If it's good, plug the EGR vacuum and go drive it.

O2 maybe, however since it's OBD I.... I'd get a scanner on it and see if it's happening in open loop or closed.

First indication is Coolant Temp Senser, Map Sensor, Fuel Pump, Dirty throttle body.

If you've got 150k on the car, you might do well to pick up a Walbro 255 fuel pump and install it. You'll have a fresh pump, and it will handle all the mods you ever throw at it.

fiveoformula · Posted: Thu Feb 05, 2009 9:27 pm Post subject:

I have had alot of problems with the EGR, I have it bypassed right now because when I plug it in it has a flat spot in the throttle, maybe Ill pop it off, clean it ans put in a new gasket...

As for recent parts I have installed;
02 Sensor
V power NGK's
Taylor wires
Fuel filter
cleaned K&N
MSD cap & rotor
Complete throttle body rebuild 2 days ago (made it a little better)
Re-man stock injectors
EGR solenoid

fiveoformula · Posted: Thu Feb 05, 2009 9:29 pm Post subject:

fiveoformula · Posted: Thu Feb 05, 2009 9:32 pm Post subject:

Boostd1 · Posted: Thu Feb 05, 2009 9:42 pm Post subject:

chevymad · Posted: Thu Feb 05, 2009 9:45 pm Post subject:

Worked on alot of tbi trucks. They can get that flatspot due to the egr too. Easiest way to get rid of it, is by using an aftermarket egr valve. There are actually 3 different types of egr valves. All differ in the way they open. Most aftermarket ones are positive pressure valves, whereas the stockers are usually negative. This should be engraved in the top of the stock valve. The positive valve requires exhaust pressure to exist before it will open. The negative does not. This means a positive valve will not open early, even if there is vacuum to the pod.

chevymad · Posted: Thu Feb 05, 2009 9:45 pm Post subject:

That is the AIR injection tube. All EGR passages are in the intake on a v/8 of this vintage.. unless you own a vette.

Boostd1 · Posted: Thu Feb 05, 2009 9:51 pm Post subject:

fiveoformula · Posted: Thu Feb 05, 2009 9:51 pm Post subject:

fiveoformula · Posted: Thu Feb 05, 2009 9:55 pm Post subject:

chevymad · Posted: Thu Feb 05, 2009 9:56 pm Post subject:

Purpose was to burn off the unburned hydrocarbons as they came out of the exhaust port. There's usually a line that goes to the cat as well.

Boostd1 · Posted: Thu Feb 05, 2009 9:56 pm Post subject: