rough idle and very slight miss


New Member
Jun 14, 2018
Peoria IL
ROUGH IDLE (slight miss)
<<<steps taken>>>
1.o2 sensor Bank 1 sensor 2 (donstream) and New MIL o2 sensor deletes added in place of old ones due to CEL code thrown
2.Oil Changed Mobile 1 5w20 with mobile one filter
3.Spark plugs motorcraft platinum (originally gapped at .54 then regapped at .45 to improve spark)
4.Throttle position sensor (TPS) swapped
5.Intake Air Control (IAC) swapped
6.Coil Packs (motorcaft) swapped
7.Wires (MSD 8.5mm) swapped
8.Mass air swapped ran worse so swapped back
** Discovered gas was in oil and fumes were recircualting back into intake from PCV causing idle to be worse
9.Injectors (Accel 24#) swapped upper plenum gasket
11.cleaned upper intake and all channels
12.IAC adjusted (raised) by 10% and adjusted throttle body to rise low idle from 675rpm to 750-800rpm
13.Compression Check... all were perfect and extremely close tripple checked
(1=179, 2=180, 3=180, 4=180, 5=180, 6=180, 7=180, 8=179)

others issues that need tending to...
I've owned the vehicle for 2 weeks. previous owner had cleaned the throttle body and washed out the coating inside the throttle body and adjusted the stopper screw (I could tell cause the blue Loctite was missing and I could see where the threads had pliers taken to them. also the intake tube is permanently bent due to the stoke intake tube being partnered up to a fender well cold air. any suggestions would be appreciated. I've exhausted so many options and so much time in the past two weeks I'm losing my mind. what else could it be. noticed a small pool of oil in the lower intake when upper was taken off. I got deal of a life time on the car and now its turning in to an average priced cobra at this point after all the money invested.
  • Sponsors(?)


Founding Member
Mar 2, 2001
Hagerstown, MD
What about the lower intake gaskets? It does sound like a leak. My bet was on coil paks and wires but you covered that...unless I missed it-what year cobra? Hopefully you dont have to deal with IMRC plates...