Chrysler Repair: Hesitation and erratic idle after slowing -- injectors?, oil pressure gauge, exhaust gas recirculation valve

Question
QUESTION: Hi Roland,

Thanks for all the advise you've posted for others -- it's helped keep my car on the road!  I'm having some symptoms that I'm not finding answers to and wanted to get your opinion.

The Car:  1991 LeBaron (AJ), 2dr convertible, MMC 3.0 A/T

The Symptoms:  After driving, particularly following a good run on an expressway then when I slow to an idle (750RPM) at a stoplight, simultaneously, my voltage meter sputters, drops for a second, regulates back to normal and the engine briefly loses power. During the entire time idling, the check gauges light remains on.  As soon as I begin to accelerate (or if I rev to >1000RPM while sitting) the light goes off, and all symptoms are gone until I idle again.

I have checked the Fault Codes, the only ones present are 12 and 55 -- so basically, nothing.

Until last week, the above scenario also included my oil pressure gauge dropping when idling, your advice to other people led me to believe it was the Oil Pressure Sensor, and I had a mechanic change that.  

I have recently changed (myself) all the spark plugs, cables, distributor and rotor trying to alleviate the issue thinking it was a misfire, but that didn't make any difference.  The mechanic suggested it may be my fuel injectors.  

What are your thoughts on that?  Would a faulty injector result in such symptoms, or is there something else I should be looking into.  If it is the injectors, would you think that's something I could replace myself -- and how does one go about doing that, since they're tucked away so neatly under the manifold? (I'm a novice, but I have good mechanical strengths, and access to most tools.)  

Thanks, in advance, Barrett

ANSWER: Hi Barrett,
I suspect the issue is one of fuel/air mixture when coming down from high rpm's to idle. Was the car by chance sold originally in California? If so it would have an egr (exhaust gas recirculation) valve that could very well be sticking ajar which will cause such symptoms without setting a code. Another possibility is a positive crankcase ventilation valve that is similarly sticking. Those are cheap and easy to replace. I doubt it is the injectors. Take a look at the MAP sensor (located on the alternator mounting bracket) and make sure that its vacuum hose is not cracked or loosely fitting to the nipple at each end. Those and anyother vacuum lines attached to the intake manifold should be checked. Use the underhood sticker as a road map to find all the possiblities where there might be a vacuum leak.
Please let me know if you have the egr and I'll give you the instructions on how to check it out.
Roland


---------- FOLLOW-UP ----------

QUESTION: Hi Roland,
Thanks for the quick response.  I've looked to see if there's an EGR valve, which there is not -- the car was originally sold for the Canadian market. I picked up a PCV valve this morning and popped it in, the old one was pretty gunked up, but the new one does not seem to improve the drivability.

As for the MAP sensor, the hose leading into it is in good shape, and a preliminary look at the rest of the vacuum lines do not show signs of cracks or loose fittings.

One other symptom which I probably should have mentioned was that the car stalled out on me a few days ago. It's never done it before.  I tried to restart, the engine turned over fine, but promptly turned off.  The electricals remained on, but the engine didn't.  I tried a few times, it turned over then died. If I gave it gas (to about 2000PRM) while it was turning over, it would remain running until I took my foot off the pedal. I then got out, opened the hood, poked around (read: stared blankly) and pressed on all the spark plug boots, (#6 on the cap seemed loose, so i pushed it firmly) got back in and restarted, and it restarted fine and returned home.  I didn't mention that earlier because I assumed it was just related to a possibly loose spark cable boot.  Although it might be valuable to the diagnosis.

Much appreciated, Barrett.
(ps, no rush in responding, I will be out for the day)

Answer
Hi Barrett,
I would check over the vacuum lines. And the other maintenance to do is to clean out the throttle body throat and idle by-pass passageway, and also both sides of the throttle plate. Heavy crud in that area can mess up idle as well. If that doesn't do it, then I would keep watching for codes.
Roland