90 MM Rough Idle And Bad Gas Milage **** UPDATE Partial Solution ****
UPDATE with Partial Solution in post #13
I have a 90 MM with 145k and I have been having a problem for about 5 months. I noticed my idle was getting rough and then the gas mileage started to get bad fast. Gas Mileage Chart I was averaging 22-25MPG and now its down to 10-14MPG. My guess is bad AFM but I don't know how to check it, is a 90 with the big round filter and square wiring connector. I have access to a AFM from a 91 but the plug a different shape and there is an extra wire in the plug.
http://dl.dropbox.com/u/34054098/201...2010.35.41.jpg
A quick list of what I have done and if it made any difference:
Made sure all sensors were plugged in and wires looked good - all good
Cap, Rotor, Plugs - No change
Checked for vacuum leaks with starter fluid - no leaks
Unplugged air flow sensor - MPG went from 10 to 14 MPG still idles rough
Swapped engines with known good engine from a 91 (old engine ate timing belt), kept existing ECU, AFM, O2 Sensor, fuel pressure regulator, wiring harness from the 90 - idles at 2k with AFM plugged, idles rough when not, MPG same as old engine.
Any ideas on what else to try or how to test the AFM?
**** UPDATE Partial Solution ****
Here is an update with a partial solution to the problem I was having.
I have averaged a consistent 11-12 MPG for the past 10+ tanks, no change from cooler weather to hot Phoenix summer temps with the a/c on full time. My dad (Dave the dude on here) has always said if its a weird problem its probably the ECU. He got a capacitor replacement kit from Mach V Motorsports and I soldered them my ECU. One capacitor was noticeably leaking but I replaced them all anyway. Here is more detail on the general problem with the ECUs.
I'm still on my first tank but have 220 miles and still over 1/4 tank left. I was topping out at 150 on a tank before.
Problems I still have:
High idle - idles between 1400-1800 rpm
Low power under 2500 rpm - it runs smooth with no hiccups but is gutless when accelerating