Idle issues... Can anyone help?

[PsYLenT-G]

My father just gave me a 91 GT last week... it has a few problems (mainly stemming from letting my step-sister drive the car for a prolonged period... dumb b*tch) but overall is a very strong running machine.

The problem I'm trying to correct now is when I first start the car it idles extremely low (probably like 400-500) and will completely die if I take my foot off the gas. If I let it warm up some, it will eventually stay running (but still under 700 RPM). When I take my foot off the gas it will surge... sounds like it's gonna die, but then picks back up... over and over. Once The car is compeltely warmed up, there is no idling issue.

I'm used to working on old-school cars... 1972 and older... so a lot on this car eludes me. I just bought a Haynes manual for it but unfortunately it really doesn't discuss this problem I'm having. Troubleshooting from an old car perspective, I'd normally look to the choke as the problem... but as I've said... not at all familiar with EFI engines.

Any suggestions?

TIA

Gary Lewis
Columbus, OH

1991 Mustang GT (stock)

 

[NKau]

Best thing you can do is get your hands on a code scanner, or take it to a shop that can pull the codes from the computer that might indicate the problem(s) for you (shops usually charge around $60 for this). This will tell you if you if any of the various sensors on the car are bad. It's a good starting point anyway.

 

[Fox Saleen 163]

I say do the basics if it hasn't already been done. Replace plugs, wires, cap, rotor, 02 sensors, fuel filter, clean the MAF sensor, replace air filter, and clean the inside of the TB real good. Even if it doesn't fix the problem it probably needs done anyway.

 

[cougar5.0]

First thing I would do is take the IAC off and clean it,then claean the TB. Then give your TPS a check with the volt meter. set it about .96-.99 volts. If the check engine light is not coming on there is a good chance there are no codes or the light is burned out .
I see you are from Columbus ever come up to Norwalk raceway? or Dragway 42?
I live about 2.5 miles away on Lake Erie.

 

[Notchbck93]

Why dont you simply turn up your idle?

How?

Unplug the IACV and set the idle screw underneath the throttle body. Once you have figured out your desired idle. Shut the car off and disconnect the battery. Give it a few mins, rehook the batt cable and plug in the IACV. Restart the car and see how it idles.

After all , its a free try. And what cougar said about the TPS ,, check it as well, perhaps it may be the first thing you want to check.

Cleaning the throttle body also helps.

Let us know how you make out.

 

[cougar5.0]

I really would not mess with the base idle screw,the idle should be set with the TPS. And if you do happen to turn the base idle screw you should always check the TPS. And notch is right alway disconect the - batt. cable and I know this is going to sound odd but once you diconect the cable turn your headlight switch on and off a few times,this will drain any current that is left in the system.

 

[PsYLenT-G]

wow... this was my first time/first post here. you guys are awesome! thanks for the quick responses. this baby is due for some MAJOR TLC. I'll post an update ASAP.

thanks again!!!

P.S. (Cougar5.0) never been to Norwalk or Dragway 42. call me sheltered

 

[PsYLenT-G]

er... while I'm here, can you guys make any recommendations on subframe connectors? I don't have the resources to have them fabricated, but can pay to have them welded. I heard the bolt-on's suck much arse...

 

[Deths91Gt]

So how is the idle now??

 

[Fox Saleen 163]

I have the Maximum Motorsports full lengths. No complaints, really stiffened up the car.

 

[NKau]

Stay away from the bolt in sfc's if at all possible; get the weld in ones if you can afford it. Also, look for the full lenght connectors that have the brackets that bolt to the bottom of your seats.