fluctuating idle only when cold????

Hozer 88GTConv · 11-14-2005, 06:19 PM

Okay,
I know idle rpm has always been a popular topic, but this one is stranger than the usual one.
Only when cold, my idle is all over the place, then the engine will just die. Start it up, and the idle goes everywhere and then almost cuts out then shoots back up again.
Once the engine is at operating temp, it idles perfectly.

I've cleaned the IAC, TB, MAF, and air filter. This just started three days ago.
I'm going to replace the ect and check/clean the tps. Is there any way to troubleshoot the MAP sensor?

It bucks now while trying to hold steady cruising rpm's 2-3k...I'm starting to think fuel pump maybe???

It just dies and then comes back all of the sudden...

Figure this one out...
thanks...

Hozer 88GTConv · 11-14-2005, 09:39 PM

Update:
I cleaned the MAF again, this time with electronic parts cleaner, not carb cleaner.
I also re-set the tps, it was reading .946 vdc, now .986.
The fuel pump seems to be fine, I hear the prime clearly everytime I turn the ignition.
Took it on a short night test run and it seems okay, real test tomorrow...

Lethal5Oh · 11-14-2005, 10:37 PM

If cleaning the MAF doesnt fix your problem, look for vacuum leaks. If you have a leak its gonna run like crap when its cold, and decent when its warm. Good luck

HoodStrype · 11-15-2005, 10:56 AM

I have the exact same problem. You can hear my vacuum leak though... somewhere around the lower intake. Good luck!

mpj76 · 11-15-2005, 11:05 AM

The leak might be coming from the hose that runs from the underside of the upper intake manifold, out towards the front, to the Evaporative Emmisions Canister (happened to me).

Hozer 88GTConv · 11-15-2005, 09:18 PM

Fixed!
Idles perfectly 750 rpm, dead steady.
I thoroughly cleaned the MAF by pulling the electronic unit out and cleaning it with electronic parts cleaner.
I also lubed the throttle body linkage assembly to ensure free movement.

thanks for the tips...

11-14-2005, 06:19 PM	#1
Hozer 88GTConv Registered Member Join Date: Feb 2002 Location: Jacksonville, FL Posts: 706	fluctuating idle only when cold???? Okay, I know idle rpm has always been a popular topic, but this one is stranger than the usual one. Only when cold, my idle is all over the place, then the engine will just die. Start it up, and the idle goes everywhere and then almost cuts out then shoots back up again. Once the engine is at operating temp, it idles perfectly. I've cleaned the IAC, TB, MAF, and air filter. This just started three days ago. I'm going to replace the ect and check/clean the tps. Is there any way to troubleshoot the MAP sensor? It bucks now while trying to hold steady cruising rpm's 2-3k...I'm starting to think fuel pump maybe??? It just dies and then comes back all of the sudden... Figure this one out... thanks... __________________ 1988 GT Convertible 331 10:1 TW heads, GT-40 intake, MSD, TRW flattops, B Cam w/ 1.7's, MAC exhaust, 24's, 70 TB, 76 MAF, 3.73's, Pro 5.0, Koni's, Anderson PMS, Wideband 02, yatta, yatta... One week with new motor, two speeding tickets...joy Last edited by Hozer 88GTConv; 11-14-2005 at 07:51 PM..

11-14-2005, 09:39 PM	#2
Hozer 88GTConv Registered Member Join Date: Feb 2002 Location: Jacksonville, FL Posts: 706	Re: fluctuating idle only when cold???? Update: I cleaned the MAF again, this time with electronic parts cleaner, not carb cleaner. I also re-set the tps, it was reading .946 vdc, now .986. The fuel pump seems to be fine, I hear the prime clearly everytime I turn the ignition. Took it on a short night test run and it seems okay, real test tomorrow... __________________ 1988 GT Convertible 331 10:1 TW heads, GT-40 intake, MSD, TRW flattops, B Cam w/ 1.7's, MAC exhaust, 24's, 70 TB, 76 MAF, 3.73's, Pro 5.0, Koni's, Anderson PMS, Wideband 02, yatta, yatta... One week with new motor, two speeding tickets...joy

11-14-2005, 10:37 PM	#3
Lethal5Oh Registered Member Join Date: Jun 2002 Location: Portage Posts: 239	Re: fluctuating idle only when cold???? If cleaning the MAF doesnt fix your problem, look for vacuum leaks. If you have a leak its gonna run like crap when its cold, and decent when its warm. Good luck __________________ '95 GT convert. K&N, C&L mass air meter, Performance distributors sreamin demon coil, dyna mod, live wires, king cobra clutch, flowmaster american thunder exhaust, UPR billet adjustable shift handle, Crane Cams Fireball HI-6 box,underdrive pullies, 255lph fuel pump, UPr short throw shifter, caster camber plates, 03 cobra lower A arms, bullit suspension, cobra front brakes

11-15-2005, 10:56 AM	#4
HoodStrype Rearview Mirror Haze Join Date: May 1999 Location: Huntsville, Alabama...a.k.a. "HuntsVegas" Posts: 387	Re: fluctuating idle only when cold???? I have the exact same problem. You can hear my vacuum leak though... somewhere around the lower intake. Good luck! __________________ 93 lx Notch 01 GT ...the epitome of Murphy's Law

11-15-2005, 11:05 AM	#5
mpj76 Registered Member Join Date: Sep 2002 Posts: 158	Re: fluctuating idle only when cold???? The leak might be coming from the hose that runs from the underside of the upper intake manifold, out towards the front, to the Evaporative Emmisions Canister (happened to me). __________________ 91 Coupe: FMS 1 5/8 unqual shorty's, BBK off road X-pipe, Super Duty T5, Pro 5.0 short shifter, 2.73 rear, G3 alt, MSD coil, dist, no smog pump, oil cooler, 195K miles, 14 deg timing, 23 mpg city/29 mpg highway @ 65 mph.

11-15-2005, 09:18 PM	#6
Hozer 88GTConv Registered Member Join Date: Feb 2002 Location: Jacksonville, FL Posts: 706	Re: fluctuating idle only when cold???? Fixed! Idles perfectly 750 rpm, dead steady. I thoroughly cleaned the MAF by pulling the electronic unit out and cleaning it with electronic parts cleaner. I also lubed the throttle body linkage assembly to ensure free movement. thanks for the tips... __________________ 1988 GT Convertible 331 10:1 TW heads, GT-40 intake, MSD, TRW flattops, B Cam w/ 1.7's, MAC exhaust, 24's, 70 TB, 76 MAF, 3.73's, Pro 5.0, Koni's, Anderson PMS, Wideband 02, yatta, yatta... One week with new motor, two speeding tickets...joy

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