The classic rough idle - seeking possible time savings

[guitarguy]

So I shelled out $1500 for a 93 with 149,000 miles for fun. Deal point was the fact that the body (man are these bodies and paint solidly built) is rust free, in NE Ohio. Hoping to be a winter car for this winter, after some shocks and winter tires.

Anyhow, it has the rough idle, shocking. I have a 94 q and I won't begin that story, but I'm no stranger to the rough idle causes and have done the research in the past (many brain cells ago). I'm a smart guy but a novice hack with cars.

I'm starting this thread to tap into the infinite wisdom of you guys and to see if I can possibly eliminate any items and pinpoint the problem before I actually do anything as I just drove the car home tonight.

Cold start, the car idles higher as it should and somewhat smooth. After fully warmed up, the car idles real rough in drive at 650rpm, a little less rough in neutral at 850rpm. When in drive at idle and real rough, the tac does not fluctuate. It maintains a steady idle speed....the vibration is almost like the really slight rhythmical vibration you feel in an american (maybe other makes idk) v6 just with the exhaust flexing if anyone knows what I'm talking about, only amplified to the point that I feel my body shaking. Under acceleration and cruising, the car feels awesome for a 19 year old Japanese steel hunk with 150k miles.

Does this description eliminate out the ACC, MAF, TB, anything? Is it obvious one or more injectors need replaced? I haven't even fiddled around under the hood yet. It was dark when I got home.

Just figured I'd round up a couple opinions before going about my business. Thanks for your time!

[OwnerCS]

The easiest things to check right off are:

1) MAF - easy to take off and clean with spray cleaner.

2) Ohm test injectors - search for Injector Ohm test for the procedure from member goody90q45.

3) Check spark plug wells for oil build up and failed plugs.

4) While the plugs are out, if you have access to a compression tester, it can't hurt to know the readings for each cylinder.

Here's a thread about my V8 becoming a V6 and the cause.

post5733011.html?hilit=v8%20became%20a%20v6#p5733011

[maxnix]

The easiest things to check right off are:

1) MAF - easy to take off and clean with spray cleaner.

2) Ohm test injectors - search for Injector Ohm test for the procedure from member goody90q45.

3) Check spark plug wells for oil build up and failed plugs.

4) While the plugs are out, if you have access to a compression tester, it can't hurt to know the readings for each cylinder.

1.) Usually a waste of time unless non OEM air filter has been employed, especially a K&N. Easy to do more harm than good.

2.) Do this first. Then measure FP pressure at WOT and idle.

3.) If you don't have a maintenance history, they and all fluids and filters are replaced immediately.

4.) IF you are not burning oil, it's an academic exercise.

[goody90q45]

........Does this description eliminate out the ACC, MAF, TB, anything? Is it obvious one or more injectors need replaced? I haven't even fiddled around under the hood yet......

I'm betting it all on bad fuel injectors. Final answer.

Ohm test the FI (and the KS) and tell us what you find.