Been having a problem with my engine rpm jumping not only at idle but through the entire rpm band. acclerating , slowing down , idling. doesnt matter it always jumps. Its not really noticible when driving most of the time and its only small jumps yet its constant. no codes , replaced pcv valve "but not the pcv filter" and it seemed to stop but after a few hours started again , checked the vacume lines and all are fine. Put STP fuel treatment and injector cleaner in it , neither helped. Havent checked the fuel filter but wasnt long ago changed it. Car does start fine and run great other than the engine surging. Anyone have any other ideas at the problem.

 

In my case, the most of idling disorders are because of broken vacuum lines, MAF sensor, and IAC valve. I have no clue if your car has MAF sensor, so try to see those components. Give us more details about your car and what you did on it, so more people could share more info.

 

1991 RS , engines the stock 3.1 no modifications have been done to the engine. recently replaced map sensor and PCV valve. checked vacume lines. Changed the fuel filter about 5 months ago and injectors were put in about 8 months ago along with a new ECU. I dont think mine has the MAF , think thats only on 2.8's 5.0's and 5.7's , not 100% sure on that but thinking thats the only ones. Also wouldnt an IAC malfunction cause the computer to give the code 35? The surging is only 80% of the time , sometimes the engine runs smooth for awhile then starts and doesnt stop for a long time , then starts again. seems to do it more at higher speeds.