ron mcatee

I need a little advice. I put in a new distributor cap and rotor, have replaced the seals on the injectors, have Magnecore wires, but still have an erratic idle, sort of like a miss. I also had the CO reset, but it still persists. Once past idle and up to Red Line the car runs great. Is it possible the Oxygen sensor could be bad? It is the original one with 118,000 mi on it, but looks OK. When I disconnect the sensor from the harmess, I get no appreciable change in the engine (sounds the same whether plugged in or not. When I first got the car 8 years ago, when I unplugged the oxy sensor, the motor idled up and smoothed out, but won't do it anymore. Any recommendations or possible checks I can do to find the anomoly? How do I determine if the oxy sensor is good or bad? Thanks in advance.

Biff Bradley

Check for vacuum leaks. Also check that the bolts holding the intake manifold to the heads are not loose. You can get at all of them if you take off the airbox. Could also be the gaskets between the head and the intake.

Mike Murphy

What do your plugs look like? How old are they? Mine idles a little rough, but I kind of like it. I can occasionally hear it miss at idle, but it happens very rarely and only if I listen closely.

g-50cab

clean all the grounds - transmission strap, engine ground behind the blower motor - battery ground - sandpaper to the connectors. Pull the wire of the coil and clean up that to with a liitle sandpaper.

Take off your idle control valve and flush it out with brake cleaner - then reinstall.

Try that first before you start replacing any expensive parts.

madmmac

When an O2 sensor goes bad the engine usually lopes the idle slowly up and down a little bit as the cycle time in the sensor is just not as fast as it should be....at close to 120k...go ahead and replace it when you have the extra $$'s laying around.

Was the car missing at idle before you did the tune up?

Did you get the injectors cleaned and flow tested or did you just replace the seals?

Make sure you have the plug wires pushed into and seated in the distributor.

Park the car outside and let it cool off. Wait until dark, open the engine lid and start the car....check to see any arching along the wires .

ron mcatee

I've done all the things all of you have suggested except for the O2 sensor replacement. Madmmac, I did not have the injectors flowed, only replaced the seals because #5 was leaking at the head. Only reason I did all four was to ensure the rubber was good because it deteriorates over time.

ron mcatee

I had a typo on my last reply. Should have read "Only reason I did all six was to ensure the rubber was good because it deteriorates over time".

Peter Kelly

I chased the same problem for a while. Turned out to be a sticking injector at idle. I found it by letting the car idle and I go under it and measured the exhaust header temp (using IR temp gun) on all of the cylinders. At idle the one cylinder was not firing but ran ok at higher revs. I verified that it was injector by swapping the cyl 5 and 6 injectors, problem follwed the injector. Replaced injector and the problem was fixed.

Mike Murphy

That's pretty smart - I will have to remember that trick.

theiceman

Now THAT is good troubleshooting ...

ron mcatee

Kelly, thanks for the info. I'll see if I can do it.

rllevin

This may be a little too simplistic but have you checked to make sure the seal on your oil filler cap is working? If the seal is missing or seriously deteriorated your idle will be slower and erratic. Happens everytime I use the dipstick to check my oil with the car idling. The seal's a buck seventy five at Pelican.
http://www.pelicanparts.com/catalog/...pg7.htm#item30