strange RPM's after starting up warm

[quapouh]

Need some help guys ...

Car starts up fine, drives superb, no problems whatsoever but one. When I park it go to the store or smth and back in 15-30 min and star it up when stil warm [between 1/4 -3/8 of the temp gauge] starts right up [half-crank] but RPM's drop down to 500-550 and it chokes little bit - after 10 secs everything back to normal it ups the RPM back to normal. Is there a specific reason it does that ... is there something out of adjustment?

it's a 89+ 7mgte with 5sp. Sparks, wires, maf, fluids everything checked or brand new. No vacum leak of my knowledge, even changed crank ven hose [we know those hard ass cracked bastards]. Stock BOV, and everything basically stock.

... help

Mike

 

[boost fiend]

minew does that too. check the isc. im lazey so i have yet to do mine.:evil2:

 

[miggles]

has it got anything to do with fuel vapour lock or heatsoak that the fuel vapourises as soon as it hits the back of the valves?

 

[lagged]

Fp Vsv.

 

[boost fiend]

mine only happens first thing in the morning. not so much after its warmed up.

 

[GrimJack]

Had to edit the thread title, it was driving me NUTS seeing RPM spelled wrong.

 

[Silent Smith]

I'm getting the same condition on my car. It's winter here and I turbo Time the car (2:30). My thought was it was headgasket ceeping(sp?) coolant into one of the combustion chambers. Could be wrong but it may be worth checking out

 

[PorterzSupra]

Anyone think of leaky injectos?

 

[lagged]

my head just exploded. let me pick up the pieces and try to reformulate my faith in humanity.....................

ok, the thread starter is describing what IMO sounds like trouble idleing during a HOT START condition. this is USUALLY caused by a non functioning FPR VSV. the purpose of this device is to up the fuel pressure in order to combat hot start problems caused by fuel boiling in the rail.

boost fiend, your problem sounds like a COLD starting problem. check your CSI and CSI switch.

 

[Silent Smith]

"USUALLY caused by a non functioning FPR VSV"

I've checked the TSRM and coud not locate anything to checking that. do you have a meathod to check it out? thanks

 

[jetjock]

"USUALLY caused by a non functioning FPR VSV"

I've checked the TSRM and coud not locate anything to checking that. do you have a method to check it out? thanks

It's in the book but the deal is that during a hot start the ecu will (because it knows coolant temp) use the VSV to disconnect the FPR hose from the intake manfold and keep it vented to atmospheric pressure. This causes the fuel pressure to stay high until the ecu again connects the FPR to the manifold (around 2 minutes after start). So you can either check fuel pressure, use a vacuum gage in the line, or check the VSV signal. Best is to check vacuum and go from there.

This sypmtom can also be caused by all sorts of other things but I suppose the FPU system is as good a place as any to start.