idle problem

sparrow_21 · Feb 7, 2003

The car is a 1988 gt convertible, 5speed. At idle it wants to jump between 500 and 1500 rpm, just up and down ,,, up and down.. sometimes killing the engine. Sometimes it idles great. At normal driving rpm I dont notice this at all. And after it warms up the problem goes away..

What would be a logical troubleshooting sequence of things to look at.. and in what order?

Thanks for any advice, input, and comments!!

jony3bravo · Feb 8, 2003

You must have recently had your battery disconnected. Which resets the computer. The 88 is a speed density computer. It has a hard time learning how to idle with new mods. But it will learn. Until the next time to unhook the battery. I have this problem all the time with me 87. I'm thinking of switching to mass air.
What I do is hold the gas pedal at about 1,000 rpms for 30 seconds or so. Then it starts to idle. Good luck

sparrow_21 · Feb 8, 2003

I have tried holding the gas to about 1000 to 1500 rpm for a few seconds then letting off... Most of the time it will "bounce" around till it either dies or evens out and idles smooth. Is it possible I have a bad/dirty injector? What is interesting is how after the car has been running for about 15 minutes.. it idles great the rest of the time...

BSL · Feb 8, 2003

Bad idle

I would suspect a MAP problem or IAC. Make sure you have no vacuum leaks! Try unpluuging your MAP sensor when its idling wierd. Your local dealer would probably diagnose this for 1 hour labour.

sparrow_21 · Feb 8, 2003

What does Map and IAC stand for? I have the Haynes service manual and I can figure most things out.

If I unplug the MAP sensor... what am I listening for?/looking for?

Thanks again

BSL · Feb 8, 2003

map iac

Manifold absolute pressure
Idle air control
Your Map sensor compares the pressure, (or vacuum) in your intake manifold to atmoshperic presure. with This info the computer can figure out how much demand the driver is putting on the engine, and how much fuel to deliver.
If you unplug it while idling it should smooth out if the map sensor is sending bad info.
I would check for vacuum leaks first! Its worth the expense to pay someone who knows, (A good mechanic). You might even learn something from him/her. Dont be afraid to ask questions. Good luck

91ConvLX · Feb 8, 2003

If you have adjusted the hard stop screw on the throttle body at all then you are screwed. If not then try the suggested fixes above.

sparrow_21 · Feb 9, 2003

Ill try unplugging it while idle-ing. I assume I just unplug the electrical connection.

If I unplug it and this fixed the problem.. can I leave it unplugged until I replace it so I dont have the car dieing everytime I come to an Idle?

sparrow_21 · Feb 9, 2003

Update on idle problem:

After the car warms up it does NOT go away.. It is just random.. Sometimes it idles... Sometimes it surges..

Ill try unplugging the MAP first then see what happens. I am also going to try the 10 wire connector fix too.

I just want to say thanks for your help. This mustang community is very helpful and intuitive.

Keep it up

sparrow_21 · Feb 11, 2003

fixed!

Ok the surging idle has been fixed! It turned out to be a cracked vaccuum line that connect to the MAP sensor...

Thanks again everyone for the input and help!

BSL · Feb 11, 2003

Cool.

Nothin nicer than a cheap fix

idle problem

sparrow_21

jony3bravo

sparrow_21

BSL

sparrow_21

BSL

91ConvLX

sparrow_21

sparrow_21

sparrow_21

BSL

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