weird idling

[project nightmare]

I have a 96 Tahoe with the 5.7 Vortec. After parking it, I can start it up and it idles weird. It will idle up and down from 500 rpms to 1500 rpms until I give it some gas for a few seconds. Any ideas?

 

[MO Viet Vet]

Get the throttle bore cleaned and clean the MAF sensor after you buy cleaner for the MAF at a parts store. Can use carb cleaner and a CLEAN rag on the throttle bore. Do not open the throttle bore to WOT. Have another person in the driver's seat hold the gas pedal down so you can reach in there and clean all around where the throttle plate closes. But not WOT!. Be prepared for the idle speed to be higher than normal till it relearns to idle. I have seen that take as little as a 1/2 hour drive or 2-3 days. Need to look for any vacuum leaks also. Maybe even a leak at the egr valve. If you are not sure of all of this have a qualified tech do it. Any CEL on?

 

[Sp8race1010]

why not open it to WOT? will it damage the tbp sensor?

 

[MO Viet Vet]

Some older engine models it doesn't matter but I have just gotten in to the habit of just saying it for all of them.

 

[rockenthebowtie]

Raiderron although those can be some initial checks as far as checking the basics, sounds more to me like he may have a leaking fuel pressure regulator, probably most likely going to need the CPI fuel injection system assy

 

[Sp8race1010]

mine acts like a weak battery when starting after long periods of sitting (12hrs). had battery tested and performed well. has rough idle and throws a P0300. at first I got a few B2S2 heater resistance codes. don't remember them but I cleared them a month ago and now only random multiple misfires. have some new 02 sensors to throw in if the codes come back.
I wonder if the CPI has a poppet hung open and upon rail prime it floods cylinder causing hard start, and lack of cycling to cause misfires.

 

[rockenthebowtie]

Popit valves for the most part dont hang open its on rare occasions that they do because they are spring loaded to remain shut and when voltage is applied the popit valve spring is energized and then opens, for the most part its the fuel pressure regulator that leaks on loads up the cylinders creating a extended crank

 

[lesterl]

The "Poppit" is just a spring loaded check valve, the other end of the tube in the Fuel Pressrue Regulator Body has the actual injectors.....

That being said Check fuel pressure for the missfires, static pressure, crank pressure, running pressure....

OP, you having any luck with your rig? dont mean to hijack your post.....

 

[Proxa]

By chance, is your CEL on?

 

[project nightmare]

no the check engine light is not on. I have cleaned the throttle body, and I also have a brand new set of injectors on it. all new hoses. I replaced the motor in it back in the fall, and it even did it before.

 

[lesterl]

Unplug the electrical connector off the MAF sensor, see if you get the weird idle, if you dont, pull the MAF and clean it real good.