How to fix engine rough idle

DAVIDGOPAUL

MEMBER
2002 PEUGEOT 607
4 CYL
FWD
AUTOMATIC
35,000 MILES

Car rough idle started after transmission was repaired. Car idle rpm jumps from 8 to 4rpm up and down when the brakes is applied then smooths out. We changed the fuel pump, spark plugs, serviced injectors and nothing helped. Check boaster for leak and worked fine. Serviced the throttle body from the back and still no change in performance. The throttle the body was replaced 2 months before the transmission failed so it is relatively new. If the idle drops to low while coming to a stop when the brakes is applied, the cars stalls. Please help, my mechanic has given up. What to check next?

1 Reply

HMAC300

MECHANIC
48,601 POSTS

You might check the engine for a vacuum leak like a line left off someplaceor partially cut and leaking. You might also check the valve at the brake booster that may be the problem. I'm taking it that there areno ocdes given so these are the obvious things that I can think of at the moment. Spraying around intake and throttle body with choke cleaner may show the leak. Also one other thing ot check is see if the evap cannister valve is stuck open as that would be one reason for poor idle /rough running condition.