Unhappy idle (Page 1/1)
JigglyWiblets NOV 26, 07:12 AM
Ive got a 1987 with the Iron duke and an automatic. For the longest time ive always had an issue where on a cold engine it would bog down on take off. In cold damp weather it was worse and would die if I didnt back off the throttle and ease into it. I made a post about it, tested the EGR, New battery and spark plugs/wires, cleaned up the TBI. Still no luck.

Last week it got a new symptom. A check engine lean code, a few days later once the engine warmed up and id come to a stop light, after about 10 seconds the idle would bounce between 500-900 rpm before randomly snapping back to normal. Its progressively gotten worse to the point that its died at a stop light. It always fires right back up, and its only an issue at idle. Besides that, it drives like a dream, absolutely no issues when moving. I pulled off the idle air valve and cleaned it up, tested the MAP, check for vacuum leaks, checked for manifold leaks. All that i found out is that the spark plug wires are leaking a little bit of power.

So my judgement call is that since ive never replaced the ignition coil and the spark plug wires are funky then maybe that? Im looking for any input though. Winter is starting in a couple days ive got no garage, and my day job is a mailman so black friday/christmas is about to raw dog me. Ive got about negative 3 days ago to figure this out. For the time being I just put it into neutral at red lights and holding the brake and gas
Patrick NOV 26, 05:36 PM
The obvious response would be for you to run a scan on the engine to see if any of the sensors are borderline and/or have failed... such as the IAT (Intake Air Temperature).

What is the fuel pressure while running, and how quickly does it drop when the engine is turned off?

[EDIT] And I see I've told you all this previously. You should've continued your original thread instead of starting a new one with the same issue.


quote
Originally posted by Patrick Here:

There is no ThermAC system on an '87 duke. There is an Intake Air Temperature sensor instead.

Check for trouble codes.

A failing Intake Air Temperature and/or Coolant Temperature Sensor could both affect engine performance, as it's possible the engine is running too lean when cold.

A failing fuel pump can also lead to a lean condition, as can a leaking "rubber" hose in the gas tank. Testing the fuel pressure would be a good idea.

Although this was for my '84 duke, much of it still applies to an '87... Tried three different MAP sensors, but 2.5 engine still bogs badly when accelerated


[This message has been edited by Patrick (edited 11-26-2025).]

hercimer01 NOV 27, 02:43 AM
I haven't read your post closely but I can tell you that you positively have a loose exhaust manifold bolt or 3. This has been my experience.