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Registered User
Join Date: Jun 1999
Location: Santa Clarita, CA, USA
Posts: 303
Idle Fixed

Well.... I was pretty much talking to myself on my idle thread.... trying to sort things out.... but I think I have closed in on it and thought I would share the results with others.

In short the problem was idle drop out and inconsistent idle speed on my 75, 1.8, L-jet... I had tried everything... or so I thought. I had noticed that changing the idle speed adustment screw in the throttle body did not change things quickly until I popped the throttle, at which point, the engine would settle into a new idle point. This seemed to indicate that there might me some problem upstream at the air sensor.

After studying some L-jet material on-line, I noticed that there was a richness adjustment screw in the air sensor that allowed un-monitored air to pass around the air sensor. Less un-monitored air = richer mixture. It turns out that this screw had been backed out almost all the way.... probably by the guy who smogged the car when I bought it... I screwed it in all the way.... In addition I took off the air flow sensor, and cleaned out the passage way with engine degreaser. The flap would actually stick at the far end of travel, i.e. maximum open. I also oiled the hinge after cleaning it and this seemed to eliminate all the sticking.

I pried off the plastic lid covering the sensor pot, wiring and flap spring.... nothing for me to play with there for now and resealed it with some RTV.

Got it back together and adjusted the throttle body idle screw and the idle locked right in to a nice 900 rpm. The mixture is probably too rich now at idle, but I have no more idle drop out after warm up of the engine. When I come to a stop sign, the engine will momentarily drop below 900 RPM and then rise back again to that level... it is nice to have it working.

I still have the occasional stumble at lower idle.... which I have not solved... that may be an ignition problem still.... or an injector problem... as I have some unknown injectors in #3 and #4.

Also after studying the L-jet system, it seems like you may be able to use the system for a larger engine.

First, since the air sensor monitors incoming air volume, a greater intake of a larger engine will automatically be accounted for.

If the engine/air intake speed is so large that you exceed the range of the air sensor, one could switch to higher volume injectors and/or higher fuel pressure and then, (it appears to me after looking at the electronics, wiring and spring section under the plastic cover), that you can re-adjust the spring on the airflap for greater tension so that your maximum air pull will not exceed the range of the sensor. With some tweeking I could see this working as a re-mapped stock FI system for a larger engine..... food for thought.

- Dave
Old 04-20-2000, 08:18 AM
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mejulihn's Avatar
Join Date: Nov 1998
Location: Camino, CA
Posts: 425
Great to hear you finally narrowed down your idle problem. I have read your previous posts with interest but because I have a 2.0 with D-jet, I really did not have anything to add.
Old 04-20-2000, 08:50 AM
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