Missing/ rough idle

Daddyfatbacks · 11-12-2014, 03:08 PM

Started up 88 na after work today and idle was rough like a cyl was missing. On acceleration missing continues up through rpm till 4k. Any help where to start checking is greatly appreciated. Oil level and color is good. Thnx

dodger1 · 11-12-2014, 04:09 PM

This is a tough one because there are so many possibilities. I would look for codes from the ECU first. If no codes then check for ignition problems next - plugs, wires, cap etc. A fouled plug might give a clue where to look.
Another way to go about this if the same cylinder is missing all the time you can pull one spark plug wire off at a time and watch what happens to the idle. What I mean is pull the wire off plug one (use insulated pliers made for this job) - is the idle the same or worse? - if worse put the wire back on and pull the next wire until removing a wire doesn't make any difference. This should help you find the problem cylinder. Now you just have to determine why that cylinder is missing.
Hope this helps.

nynor · 11-12-2014, 05:06 PM

hmm... can we pull codes on these cars?

i agree with the fouled plug idea. that is where i would start.

Lizard944 · 02:54 PM

Injector...almost guaranteed. Any coughing or light backfire sounds out the exhaust? Get a non contact thermometer and check the cylinder temps at the exhaust manifold. The lowest cylinder temp is the culprit. You can also try tapping on each injector with a socket extension and hammer while the engine is running.. This will sometimes free up a sticky injector.

Daddyfatbacks · 11-13-2014, 02:51 PM

Pulled the spark plugs during idle. Started from front one at a time. The first three miss got worse, the last one at firewall didn't change idle when pulled. Could hear spark jumping from wire to plug when close. I assumed was fouled plug. Got new set of plugs and installed, but idle/ midrange miss still there. Plug was caked w light brown/white deposit

DannoXYZ · 11-13-2014, 02:52 PM

No codes possible from DME.
My vote is on an intake/vacuum leak somewhere.

Do a compression-check. Might correlate those numbers with the deposits on the plug.

Daddyfatbacks · 11-13-2014, 02:53 PM

???

Daddyfatbacks · 11-13-2014, 02:54 PM

Was thinking same, will look around. Thnx

nynor · 11-13-2014, 04:58 PM

bad rotor, cap, or spark plug wire, perhaps.

Lizard944 · 11-13-2014, 07:39 PM

The light brown/white crust on your plug electrode is because that cylinder is running lean or not atomizing properly. Try tapping on that injector like I described earlier.

Daddyfatbacks · 11-14-2014, 01:17 PM

I'm thinking it is injector, because a vacume leak would not make just one cyl miss. I know it's the rear cyl missing from pulling spark plugs. Just replace injector? Anyone have luck w rebuilds? Thnx again

Daddyfatbacks · 11-14-2014, 01:27 PM

Just tried tapping injector but no improvement

Lizard944 · 11-14-2014, 03:14 PM

You have to tap the injector pretty aggressively while the car is running to get results. There is a youtube vid on it. If that doesnt work, then its probably toast. Try listening to the injector with a mechanic's stethoscope or a long screwdriver touching it and place the handle against your ear. Sound different than the rest? I really narrowed mine down by doing the temp test at the exhaust manifold. My number one cylinder was running 100 degrees cooler than the rest. In trying to track down the problem, I pulled the exhaust manifold off to have a small crack at the "Y" welded and noticed the #1 port was white ash color. Lean. Got a new set of injectors on ebay for around $120. Completely cured the problem. Symptoms were, rough idle with light "woofs" and random blasts of air out the tail pipe. Hesitation (bunny hopping) at all speeds, but worse at slower speeds. Also, revving in park up to 6K rpm sounded like the engine was coming apart. Good luck.

DannoXYZ · 11-14-2014, 05:29 PM

You can confirm injector issue my moving suspect injector to different cylinder. If the fouled plug moves to different cylinder, that'll confirm it.

RC Engineering and Witch Hunter does injector-cleaning. They'll clean and test flow-rates to match them up. If beyond repair, then you should get a complete new set to ensure they're the same.

Lizard944 · 09:21 AM

Quote:

Originally Posted by DannoXYZ

You can confirm injector issue my moving suspect injector to different cylinder. If the fouled plug moves to different cylinder, that'll confirm it.

RC Engineering and Witch Hunter does injector-cleaning. They'll clean and test flow-rates to match them up. If beyond repair, then you should get a complete new set to ensure they're the same.

Not a big fan of sending 27 y/o injectors out for a cleaning. I did this when I was having an injector problem, and when the post cleaning report came back telling me that all the injectors were good, it had me second-guessing my diagnosis. Put the cleaned injectors back in and still had the same issue. Finally bought a set of Bosch "new old stock" injectors off of ebay and it has been running great for the past five years. Four new injectors didn't cost a whole lot more than the cleaning service. I suppose the cleaning has a usefulness if you want to do semi-annual preventative maintenance. Also, match flowing injectors involves testing a large batch of injectors and picking out ones that have identical flow rates. As far as I'm aware, there is nothing on an injector that is adjustable.

Daddyfatbacks · 11-16-2014, 06:32 AM

Just found a vacuum line going to the fuel rail broken, going to replace and see if helps

Arizona_928 · 11-21-2014, 03:53 AM

I'm going to go with AFM...