Self-Revving?

[danmartinic]

This is odd

[Tom]

That's usually the TPS idle switch -- either not working or not adjusted to click. I'd start there and report back. Might have a vacuum leak too, but I'd start with the TPS. [Edit: need more coffee. Vacuum leak or idle just set too high or ISV malfunction all probably strong possibilities -- at least as likely as the TPS.]

https://www.carpokes.com/viewtopic.php?t=525#p5222

[danmartinic]

Thanks Tom

TPS clicks as normal.

I think I hear a vac leak but can't identify right now. Will have to put some time aside on the weekend to do a full test

I do have a broken manifold exhaust stud and slight leak there.. though that's been there for a while now

A restart and surging disappeared. Unplugging O2 sensor has no effect. Jumpering B&C at the diagnostic port (like when setting idle) results in significant idle drop.. but I won't adjust it until I check / fix vac & manifold leaks

I also had occassional sudden engine cutting while driving... re-soldered DME again on the weekend

Going to do same for KLR as well

[Tom]

Thanks Tom

TPS clicks as normal.

I think I hear a vac leak but can't identify right now. Will have to put some time aside on the weekend to do a full test

I do have a broken manifold exhaust stud and slight leak there.. though that's been there for a while now

A restart and surging disappeared. Unplugging O2 sensor has no effect. Jumpering B&C at the diagnostic port (like when setting idle) results in significant idle drop.. but I won't adjust it until I check / fix vac & manifold leaks

I also had occassional sudden engine cutting while driving... re-soldered DME again on the weekend

Going to do same for KLR as well

Yeah, that makes sense about a vacuum leak. The RPM's climb from the extra air but if the idle contact is closed the injectors will shut off and the revs will drop until the injectors come back on -- and the cycle repeats. I've been working on a TPS lately, so it was too top of mind. Worth testing, but vacuum leak is a more likely culprit especially if the TPS idle switch is working.

[danmartinic]

Well it's a moving vacuum leak then as it's back to normal since the restart

It started on the highway so maybe a pattern will emerge during the daily drives this week

It's diagnosing on the fly lol

[Tom]

Well it's a moving vacuum leak then as it's back to normal since the restart

It started on the highway so maybe a pattern will emerge during the daily drives this week

It's diagnosing on the fly lol

You might try wiggling the ISV connector to
see if that induces the issue. What happened on the highway -- is something wrong when cruising too? or just at idle?

[danmartinic]

I was touching & moving all kinds of stuff including ISV (what I could reach) yesterday while the surging was present and nothing changed.

Today's drive in was uneventful.. and I also notice that vacuum is perfect; I seem to recall whenever I have a leak, gauges show a little less.. isn't that right?

Might pull the KLR and resolder inside as that one has never been done

I'll pull the air filter and perform a low-pressure test for air leaks too but all this has to wait as I'm not young enough anymore to stay up on a worknight under the hood in February

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[danmartinic]

is something wrong when cruising too? or just at idle?

Just idle

It was annoying bumper-to-bumper traffic and I'm sure I got some looks lol

But even in neutral holding throttle open a bit equals no surging

[danmartinic]

The revving never returned after the one time last week.

Timeline:

Feb 14-15 - Re-soldered DME (had some occasional engine cut-outs for couple of weeks)
Feb 17 - Self-revving starts on drive home and stays until engine shutdown. Restart engine & gone
Feb 21 - Re-soldered KLR

Could not find any vacuum leaks in engine bay.. but I did find that the boost line knurled-knob attachment at the KLR was loose (though still connected)

I'll see how this week's driving goes

As an aside... it's the second time in 7 years I've re-soldered the DME (first time for KLR) and I'm again amazed how much smoother everything runs after this operation

All those strange annoyances that slowly creep up and we get used to--the 'bunny hop' at low rpm, the slight missing here and there, other strange stuff we just chalk up to 1980s normal--disappear

And for a brief time... runs like new again