Update. I got my ECU back from repair and drove with it for about a week. In park or neutral, cold or warm, the idle fluctuates from 1300 to 1700rpm at about one second intervals. When driving, it also fluctuates when coasting in gear once it gets to about 1700 rpm down from higher rpms. Switched back to the other ECU.

The other ECU does the same thing every now and then at idle, and always when coasting in gear once the rpms get to about 1500. Just less pronounced than the fixed ECU.

I don't think anything is wrong with the fixed ECU, it may be operating a little differently because of the new capacitors. Something is telling the ECU to vary the idle, since it happens with both of them. I just need to figure out what that is.

It isn't the fuel pressure regulator. After verifying that the low pressure fuel return line wasn't restricted, I installed a new OEM fuel pressure regulator. Pressure is now 40psi instead of 44psi with the old regulator, but the idle is still 1200 after warm up with the non-fixed ECU. And it still exhibits the fluctuation when coasting.

I found a JY distributor and capacitor/filter assembly last weekend, so I'll try swapping those out tomorrow.

Last edited by DirtDriver; 09/27/08 09:25 AM.
1990 Monty LS 3.0 A/T LWB. KYB front shocks, OME rears and coils. 33x10.5 BFG Muds. 5.29, 2.85, RD110, RD46. 2 bouncys. Aisins. Monte Disco swaybar disconnects. GenII t-arms, idler arm, UCA's, V45W front brakes. 2in BL.