I'm leaning towards a fuel issue.

[Marcos]

89is has taken a tiny hiccup into a bit of a stumble. At idle when cold it throws a check engine light, has misfired quite a bit lately.

Pulled 4/5/6 plug wires and no change in rythm (cyl. 1 caused immediate stall)


thoughts?

thanks

[jlevie]

What fault code(s) are stored in the DME (hint, try a stomp test)?

While this could be a fuel problem, the odds are that it will be a combination of things. Starting with the most likely causes:

1) Remove and clean the ICV (with carb cleaner) until the vane moves freely.
2) Verify the operation (electrically) of the idle and WOT switches in the TPS & adjustment.
3) Adjust the valves.
4) Replace the ignition wires, distributor, and plugs (with NGK ZGR5A).
5) If it has 100k or is of unknown age, replace the O2 sensor.
6) Change the fuel filter.
7) Have a smoke test run and fix the leaks it reveals.

A check of rail fuel pressure would be a good idea.

[Marcos]

Thanks Jim,

I pulled the plugs today and no wonder I have a misfire. 6 and 4 are covered in ashy carbon. There is a bit of predetonation signs on 2 so certainly I have carbon deposits...

From what I've read, the condition on 6 and 4 can come through the fuel or oil. Wouldn't they all be affected if that were the case?

[jlevie]

While the ash could be from fuel, it only being on two plugs tends to suggest oil as the case. In general injectors tend to fail by clogging, though they can leak. Worn rings or worn valve guides and/or bad seals can cause oil burning. Compression (dry & wet) and leakdown numbers will tell you a lot about the condition of the rings and cylinders.

[Marcos]

Re: fouled

Thanks Jim, always thoughtful and insightful advice from you.

I changed the plugs and did a valve adjustment today. The plugs were fouled so that cleared up the stumbling.

The valve adjustment sure makes the motor purr...
Very easy service, don't forget the 4 plugs!