idle problems when cold

[Tyler16]

when i start the car when cold it runs very rough at idle going up to 1500rpm then to where its about to die then back up over and over. it will also drive very sluggish. But once its warmed up it runs strong. it will also hold at 1500 rms for a few seconds then drop back down.

Im assuming I have a vaccume leak sense it holds at 1500rpm for a while but it only does it when it is cold so can i cut down my trouble shooting?

the car also misses and i checked the fuel pressure. with key on engine off it goes up to 19psi. With the engine started it climbs to 34psi. Shouldnt it stay the same? Then it jumps 2psi when ever i rev it. Then with engine off it holds. So i dont think there is a leak it just climbs slowly. But when starting the car it starts right up.

any thoughts?

 

[87GT40]

if you can find someone with a smoke machine to check for a vacuum leak. you could also try spraying starting fluid around to maybe find a leak.

 

[jrichker]

Check fuel pressure –
Disconnect the small vacuum line from the fuel pressure regulator and plug the line. Leave the port where you removed the line uncapped and open to the atmosphere.

Start the car and observe the pressure: you should see 37-41 PSI at idle.

Be sure to unplug and reconnect the vacuum line to the fuel pressure regulator when you have finished your tests.

Fuel pressure test gauge are available for rent/loan at most major auto parts stores like AutoZone.



See the "Surging Idle Checklist for help with all your idle/stall problems. Everything you need to find and fix idle problems is in there.

The first two posts contain all the updates to the fixes. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.

 

[Tyler16]

ok i had a smoke machine shoot through the system and no leaks. I also replaced the iac motor. What other sensors are used during open loop?
is the act or map sensor used during open loop?

 

[HISSIN50]

Did you pull codes yet?

The ACT and MAP are both used in open loop.

 

[Tyler16]

no codes but i think that act sensor is my problem b/c it has been relocated to the air box and im going to move it back to the intake. My guess is that the map and the act sensors are not giving each other proper readings anymore after the relocation. Maybe the readings just arnt off enough to pull a code. I don't know what do you think?

 

[HISSIN50]

The relo'd ACT should not cause issues. You are right that the ACT (even when mounted in the lower intake) can be out of calibration but not out of absolute spec. Thus no code is thrown. There's a better chance of the ECT being the issue though.