Volkswagen Owners Club Forum banner

1 - 6 of 6 Posts

·
Registered
Joined
·
4 Posts
Discussion Starter #1
89 Jetta with 1.8 single "RV" engine.

I was driving and it suddenly started running rough. Barely could accelerate as it is stumbling so bad. Pulled over shut it down and had a look (saw nothing unusual) Restarted and it purred for about a minute then back to rough. There is soot on the ground it is running so rich (none when first started).

Coolant temp sensor checked.
Fuel pump, filter and transfer pump tested (was working at night and did not know about the soot bellowing from the exhaust)
New plugs, cap, and rotor
New air cleaner.

A few days later,
It runs smooth. with full power until warm (first started) and then restarts smooth for about a minute after each restart.
My brother was falling me back home and said he could see when it started act up form the exhaust change. clear to black.

Anything hint as to where to check next?

Thanks in advance,

James (relearning VW fun)
 

·
Registered
Joined
·
4 Posts
Discussion Starter #3
update, air flow sensor swapped out, and brand new Oxy sensor installed. Car runs good with o2 sensor unplugged and horrible with it plugged in (hence why I thought it was bad)
I have sunk $300+ into her and I still runs like sh*t.. I think a match may be in order now.
 

·
Super Moderator
Joined
·
13,746 Posts
i'm guessing a vacuum leak. if you're getting too much un-metered air (vacuum leak), the o2 sensor will sense this and the computer will try to compensate by adding fuel as a safety mechanism.

when it is idling without the o2 sensor plugged, spray a mist of throttle body cleaner over the engine bay and listen for your idle to change. any change in idle from the mist will indicate a vacuum leak. if it happens to react, isolate by misting quadrants.
 

·
Registered
Joined
·
4 Posts
Discussion Starter #5
As suggested (thanks LeOn) leaks were checked for as well but all were tight and good.

After confirming the o2 was working ok and retracing all wires from the ECU for resistance valves. I shorted the CTS to simulate extreme temp and it still didn't lean out the fuel mix.(O2 was reading 0.92V). Was about to replace the ECU when I saw it......


Fixed it.. Was a ground wire below the main group on the valve cover. There were two wires below on the side of the engine. One was cracked and the other was broken. Cut them back and regrounded them and all is good again.

Make sure you clean and check ALL ground points :)

Wow 1 lose wire cost me $400 in parts grrrr. but I have loads of spare parts now
 

·
Super Moderator
Joined
·
13,746 Posts
that's cool you found it. checking grounds was going to be my next suggestion. it's usually one of the first things you check. some freaky stuff happens when grounds are loose. for instance, my wife's car (kia) was throwing bad eepromm codes (fried ecu codes) and misfiring like crazy. it was a loose ground from the alternator to the intake manifold; it took an entire minute to correct the situation.

besides, o2 sensors need to be changed more often than we tend to think.
 
1 - 6 of 6 Posts
Top