My SRT-4 has become a Ford. A couple weeks ago it started to miss at an idle and would stumble off and on during take-off, but was seemingly fine from around 1,500rpms and up. The next day it's idle was better yet not perfect and it was fine except when it was at around 7psi boost or more at which point it would fall on it's face a pop. It got to where the idle was fine and it wouldn't stumble and miss until around 10psi or more. That was until I sprayed it off at the car wash and then the idle was crap again and the cycle started over. I then drove it for over a week without washing it and it was better, but still would only get to 10psi boost because it would miss and pop/backfire. The idle miss came back even without washing the car, but it wasn't as bad and it came and went. I sprayed the car off twice without it getting worse. That was until tonight and now it's at it's worst idle miss yetwhich beganafter starting it up at the car wash after spraying it off, but this time for some reason the speedometer was going up to around 5mph even though the car wasn't moving......it wasn't even in gear.

I have checked everything visible for any damage or bad connections and found nothing. I have also checked for any codes several dozen times over these few weeks and there's none. I was hoping to take care of it myself and save myself the hassle of taking it to the dealer and being put in another POS rental car, but I'm at a loss since there's no codes, no CEL and no visible signs what so ever, not to mention the unrelated, yet somehow obviously related speedo glitch which makes absolutely no sense unless it's the PCM itself. Anybody have any ideas or should I slap a Ford emblem on it and be done?

 

change your plugs and wires

 

Nice in theory. The plugs and wires are less than a year old and functionally perfect and one of the first things I checked out. I first checked the gas, which is Ultra 94,and used a gas treatment that removes water and I checked for codes. Then I checked for any disconnected, broken cracked or frayed wires,lines, hoses, seals, etc. Next was checking the oil and pulling spark plugs. Even changing the plugs and wires to the older ones which were in perfect shape changed nothing.

 

the fact that you're saying it happens at 7psi is a very good indication that it's spark related. our spark profile changes in higher boost......actually at over 7psi. if there's a spark problem that's where you're going to see it. change the plugs and wires for new ones, don't just look at them. a yearis plenty on a single set of plugs and wires.and also see if you can swap coil packs with someone to rule that out as a problem. the reason that plugs and wires are the first thing that people go to is because the vast majoirty of the time it is that simple.

also check your tps...might be acting up. i don't remember if you fixed that already.