Will Leaky Injector Seals cause Rough Idle?
 

1989 260E

I have 3 or 4 leaky fuel injector seals that I plan to replace this week. Could they be contributing to somewhat rough idle -- with the car continuously trying to adjust fuel/air mixture?

I have an all-new and Position Sender Unit, distributor cap and rotor, STI spark plug wire set and properly-gapped Bosch copper plugs. Fuel pump relay, OVP and ignition control unit are all fine.

I have always had a slight rumble at 500-600 RPM idle, which goes glass smooth at 1000+ RPM (at which point I can't tell if I even have an engine). My assumptions are the leaky injector seals, or perhaps a dirty fuel filter (which I also plan to replace this week).

Any thoughts?

"I have 3 or 4 leaky fuel injector seals that I plan to replace this week. Could they be contributing to somewhat rough idle -- with the car continuously trying to adjust fuel/air mixture?"

Sounds plausible, but how do you know they are leaky?

Steve

Hi Steve,

My mechanic told me, and showed me, by spraying carb cleaner (??) around the leaky injectors, and pointing out the higher CO2/NO readings on an emissions test machine after the cleaner fluid burned.

Since the electrics (plugs, wires, distributor, sender unit) are all new, the OVP, FPR and coil are almost new, and the ICU is in good shape, it seems to boil down to a fuel/air mixture problem.

The leaky injectors have skewed emmissions tests and the car intermittently pumps too much and too little fuel which seems to me could also impact idle smoothness.

Sounds like a solid test. I recently inspected my injectors, when I received what were SUPPOSED to be the new injector seals. I wanted to make certain that if I damaged the old ones I had backups.

Turns out the new ones are incorrect - or a differently-designed non-oem replacement. They look like donuts instead of a shaped rubber seal. I wondered if the old ones were still sealing properly - in preparation for OUR emission test. Didn't seem worthwhile just reordering the correct seals until I had a bigger order, but maybe I'll pay the extra for the inexpensive seals and get a set at the dealer. Cheap insurance.

Steve