Question from a recent Plenum Graduate

[shaginator]

Hello.

'94 Q45 133K mi.

I just finished replacing the valve cover gaskets, cleaned plenum, replaced under-plenum hoses, cleaned throttle body, replaced plugs, changed motor oil & filter, replaced PCV valve, flushed power steering fluid, replaced belts. Worked about 3 days over 2 weekends and a few hours after work on weekdays, with lots of downtime waiting for all the parts, and going to the hardware store to buy more toys... er tools.

(Phew! That was a lotta work! Next up will be the struts and bushings on all four, and then those $39 Yokohama AVS Intermediates get put on for good measure )

Ok, now for my question...

After getting everything fixed up and back together, I nervously started up the engine. Startup was nice 'n zippy (new plugs!), but the idle was rough, and didn't smooth out by much even after a few minutes. Did a quick test drive, hoped the ECU just needed some more run time and a bit of strain to adjust everything... but after a couple of miles there's less power, and idle was much rougher.

I pulled back into the garage and inspected all the electrical connections, vacuum hoses, the TB, MAF, EGR. Everything's fine... for example, the EGR to plenum was clean and dry when re-installed, etc. All connections clean. At this moment, I'm contemplating how much I could get for a trade-in.

I realize I need to pull into the garage more to get its door closed. I reluctantly started the engine, but now it's purring perfectly. Hmph. Another test drive. Worked beautifully.

Soooo... what the heck happened? I had the battery disconnected during the repairs, and knew the ECU has to reset itself, "tune" everything up, etc. But the rough idle seemed to go away under unrepeatable circumstances. I'm worried it'll come back at some inopportune time.

Is there anything else I should keep an eye on besides the MAF, EGR, knock sensors, and injectors? Or is this kind of normal after such a lengthy repair?

[DAEDALUS]

Congrats on getting the whole enchilada back together. Your body will ache for another couple days, and by then the cuts should be about healed If the problem went away after checking all the connections, that tells me you did have a bad connection somewhere, fixed when you double-checked your work.

[Q451990]

I wouldn't say it's normal, but if the problem cleared itself up, maybe it was something you freed up in the plenum cleaning that had to be burned off? I'd lean toward an electrical connection issue (injector connection or MAF) since a vacuum leak won't fix itself, but electrical stuff sure will.

I've seen injectors get a little weak after sitting for a while... Had a near dead miss on one of the Q's after it sat for a week and a half.

Heath

[maxnix]

If it was sitting two weeks and the tank was not full, you may have had condensation in the tank, or just bad gas that the water finally precipitated out.

Did you change the fuel filter?

[shaginator]

maxnix - thanks. I overlooked that as a possibility.

Fuel filter hasn't been changed maybe 40K. Worth a change even from a pure maintenance perspective.

[Q451990]

Absolutely... I try to replace mine annualy. They're not that expensive, especially vs. the cost of even one injector!

Heath

[Q45tech]

Sometimes I have a dream about my evil twin forcing abusive owners to eat all the dirt they allow in the systems............but then reality shines thru and they are forced to spend their money or lose their money via tradeins.I heard [truth?] In the old Soviet Union if you were fortunate to have a car and abused it you were taken off the list after 6 months in prison - of course you could bribe someone.

It's going to be 7F in the morning this affects my sanity.

The point is most of the time owners are responsible for their own car problems.........of course there are exceptions.

[911/Q45]

Dennis, that is what you get for living in Atlanta. If you want to enjoy those beautiful temperate summers, you have to put up with harsh winters! I wonder how they could tell if you abused a Soviet made car, only their military stuff was of any quality.