HELP: New senerio dealing w/ bad idle

mikec

Registered User
Ok I have put in some dry gas to help absorb any moisture in the gas...To refresh our memories: When driving home from work, i came to a stop light and the check engine light came on and the car began to idle very bad. Checked the codes and replaced the dis module again and that did not fix anything. Next i replaced the IAC and gasket AGAIN and this did not help any.

The car idles to 2100 rpms upon start and falls off to 500 and then shuts off. After you get the car running by holding down the gas pedal, the car will idle around 800-900 rpms but the boost gague reads 10-20 in HG more towards the 10 side.

Thanks again for your help...What could my problem be...also the car sounds like it is missing...new sparkplugs as well.

MIke
 
check for a slight "wobble " in your harmonic balancer mine was skipping almost un noticeably a week before the balancer failed any kind of load on the pulleys like turning the wheel hard like say in a parking lot causing power steering pump to work more would cause stress on all pulleys. this may be your answer this would cause the crank sensor to go out of alignment slightly at first.(in case you wonder what this might has to do with your prob)
 
mikec said:
The car idles to 2100 rpms upon start and falls off to 500 and then shuts off. After you get the car running by holding down the gas pedal, the car will idle around 800-900 rpms but the boost gague reads 10-20 in HG more towards the 10 side.
MIke

Here is the deal. Idle speed is 100% controled by air taken into the engine. You could try and dump a bunch of extra fuel in there, but without the air nothing would come of it.

So the problem you describe has to be some sort of uncontroled infiltration of unmetered air into the intake. Unmetered means that it's getting in without the MAF sensing it.

How long do you have to hold the gas pedal down to to keep it running? It sounds like an odd problem. Check the electrical connections at the Idle Air Control unit (IAC). It may not be functioning correctly. Though why it would suddenly start working right after a bit I don't know. I guess I would be thinking IAC first but I'm not sure.

Maybe someone else has more ideas.
 
to answer mike's question about IAC

I have replaced the IAC, and the problem still persists. It is the part from Ford, not aftermarket.

Tonight, I started the car when cold and it idled to 2100, then went down to 500 and cut off. So i decided to hold down the gas pedal to get the car warmed up a little bit. After about 3 minutes i'd say I let off the gas and the car began to idle aroun 800-900 with the boost gague ready 10 in HG.

I took the car out for a drive and it began to idle high. around 2000 constantly when in gear. When I would come to a stop light it woruld idle a little lower and then eventualy back down to normal 1000 rpms.

I have no idea what could be wrong, I pretty much have a brand new engine witht the parts I have replaced.

I once again appreciate all your help.

MIke
 
Will it start with the IAC disconnected?

What happens when it's idle is up but you put it in gear. Is it able to pull or is the idle easily brought back down?
 
idle when car is in gear...

Have not had a chance to dissconnect the IAC to see what happens. I have noticed that when I drive the car, when pulling up to a stop light (keep in mind my car is a manual) when i push the clutch in, the rpms shoot up to 2000 then drops down to about 1700 id say no more than 15 seconds later and then down to 1300 about another 15 seconds later it comes close to normal aorund 1000.

While I am driving the car, it idles high, I almost do not have to put on the gas and it will cruise at 45 mph in 4th gear.

Lastly, I did notice that the tube for the air box was loose so we tightened it up and the problem went away a little bit.

Mike thanks for your on-going help. This is very frustrating for me.

If you need any other info e-mail me at mcondax@yahoo.com
 
Mike, if you have a new IAC, then you can probaly conclude that its not the problem. Sounds like you have a vaccuum leak somewhere past the TB. Check with propane around the intake tube, the back of the intake plenum, the supercharger, and the IC tube joints.
 
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