TeeterTawter

Hi, okay so i dont have a mustang but its my buddys 1990 grand marquise, it has a 5.0 with the efi and im not sure but im taken a guess its the same motor as the mustang (let me know if im wrong plz).
ever since he got the motor washed (shampoo and pressure rinsed) it has had a very rough idle and when you let off the gas the CEL comes on and goes away when u go back on the gas. at idle it sounds like the rpms are jumping. rmps will run high at times then lowers then sometimes stalls. someimtes u can just barely here the rpm change but its noticable then it just stalls, happens when the car is hot or cold, temp doesnt seem to matter it still acts up. I thought that maybe a vacuum hose got blown off but all vacuum hoses seem to be intacked and not ripped or cut... I know its not a mustang but im hoping you guys can help.

Thanks in advance

Sean.

nmerrill

Maybe the MAF sensor got wet? Try cleaninout out your sensors. Be very careful when doung the MAF. Also check your TPS voltage