Still have a strange cold start - NJFBOA - Home of New Jersey's Camaros and Firebirds

97Formula · 03-22-2012, 12:39 PM

I have a strange issue that is still lingering even after a complete fuel system overhaul (new fuel pump, power-cleaned injectors and throttle body).

On a cold start, it will fire up and rise to 1100RPM, but drops to 800RPM and stay there for 1/2 second, and finally rise back to 1200RPM and stay there until warm, then go back to 800RPM (normal warm idle). The idle speed pretty much stays put and never stalls or surges except that little bit on a cold start, but I do notice a little roughness at a warm idle at 800RPM (tach needle doesn't move but I do feel occasional "jolts" as the engine idles). When I drive normally (or drive at WOT), car runs awesome. No stumble or hesitation as I press the gas pedal. No SES light either.

Any ideas? Already tried another MAF sensor with no change. Does the throttle body power clean service include the IAC valve too? The car used to just go straight to 1200RPM on a cold start (problem did exist before having all this work done). Thanks!

jam01 · 03-22-2012, 12:45 PM

tps sensor?

sweetbmxrider · 03-22-2012, 01:48 PM

I would try tapping on the IAC and/or removing and cleaning then resetting. You turn the key on with engine off and hold the gas pedal halfway for 5-10 seconds. Then turn the key off.

97Formula · 03-23-2012, 02:55 AM

Could it be my AIR pump? The weird start seems to happen only while the engine is at a temperature that requires the AIR pump to operate. Starts up much smoother when warm.

sweetbmxrider · 03-23-2012, 07:18 AM

Pull the relay or unplug the pump itself and see if it changes.

97Formula · 09-02-2012, 11:34 AM

Hello, still seem to experience this cold start where the engine revs "surge" once briefly before staying at 1200RPM (goes to 1100RPM upon cold start, then 800 for a brief second, then back to 1200RPM until warm, when it goes back to 800-900RPM). Used to rev up to 1300-1400rpm briefly before dropping to 1200rpm when cold. Warm starts still normal (rev up to 1300rpm, then back to 800-900rpm (warm idle). This occurred before and after new fuel pump and fuel filter, as well as cleaning TB and IAC. Tried a different MAF and nothing changed.

Because I've been watching things closer now, I happen to notice a brief "mechanical" sound when the engine fires up (hopefully it's just the ABS module kicking in upon startup). The noise only lasts a split second, (warm or cold), but still have that slight surge of RPMS on cold start. Engine seems mechanically sound (hasn't been ticking as much, if at all lately).

Maybe I'm worry about nothing, since it still runs great (especially since getting the new fuel pump).

1320B4U · 09-02-2012, 10:13 PM

tps would be my guess......iac would normally cause a 'warm start idle' when cold, i.e when its cold it would start and idle at 600-7-- (or whatever your car normally idles at warm)....remember to check this connector as well..check the inside and see if its corroded on the connector (they operate on voltage and signal)

97Formula · 09-03-2012, 06:40 AM

Quote:

Originally Posted by 1320B4U

tps would be my guess......iac would normally cause a 'warm start idle' when cold, i.e when its cold it would start and idle at 600-7-- (or whatever your car normally idles at warm)....remember to check this connector as well..check the inside and see if its corroded on the connector (they operate on voltage and signal)

I may have to check the connectors (these were never removed). Cold start idle does drop briefly to 800-900RPM (for about 1/2 seconds immediately after starting), then goes back up to 1200RPM until warm.

However if there were connection issues, wouldn't I be getting a SES light (which I currently do not have)? Also, warm starts are still normal. I also tried running idle for about 2 minutes (after cold start), shut it off, then started it up and it was normal. However, if I only run for about 30 seconds, shut it down and start it back up, I get the same "rough" cold start.

97Formula · 05-01-2014, 06:36 AM

Sorry for bumping an old thread, but I still have not been successful in fixing this (may need to invest in a scanner that can read sensors like coolant temp, iac, etc). Issue does seem minor, just want to make sure it will not lead to more serious issues down the road (still runs great, no SES, and has also passed emission inspection). Just strange that the cold starts began to act like this vs warm starts.

I haven't mentioned there is a "pop" sound that occurs after turning the key and allowing the fuel pump to prime (this also happens only when cold, the pop does not happen on a warm engine).