High Idle, Hanging Idle!!!

[xMalignancy]

Ok so ive been fighting a high/hanging idle for weeks. Swapped a stock 5.0 into my stang and ever since ive had this problem. The car will NEVER be lower than 1000 rpms. EVER. When im driving normally, inbetween shifts it will hang at 1700. If i come to a stop it will die down to 1400 maybe higher. HOW CAN I FIX THIS? ive cleaned maf, changed iac, reset idle, did the 10-pin connector mod, new air filter, i cant find any vacuum leaks. what else can i do/try? Its really starting to drive me nuts! thanks for the help!

 

[jrichker]

See the "Surging Idle Checklist” for help with all your idle/stall problems. You can guess at the problem and throw parts at it, or you can use the checklist to help you find the problem quickly and inexpensively.

The quick and easy way to dump the codes is in there too, and all you need to do it is a paper clip! The first two posts contain all the fixes & updates. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.

 

[86notched]

What type of computer do you have installed? Are you 5 spd or aod? I know if you use the wrong computer it will cause your rpms to hang at every stop for a few seconds

 

[xMalignancy]

The car is a 5 speed but i swapped a motor into it that was in an auto. So its a 5 speed body with an "auto" engine. Is there something on the motor that tells it its an auto? i ran the codes and the only thing it came up with was code 34.

 

[xMalignancy]

i am reading something about the dashpot decay? It seems like that is my problem. But why would it all of a sudden change?

 

[jrichker]

The 5 speed cars use an A9L computer, auto trans cars use an A9P computer. There are internal differences in the neutral safety circuit and the computer programming. Usualy you can get away with using an A9P auto trans computer in a 5 speed car.

How much of the "Surging Idle Checklist” have you done? That's where you will find the best answers to your idle problems. It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 99,000 hits, which indicates it does help fix idle problems quickly and inexpensively.

 

[xMalignancy]

thanks man i REALLY appreciate it. Ill go through the checklist and see what i can come up with. Ill report back if i can figure it out