I'm having a wierd startup bug on my '90 GXE.

First, it starts hard in the cold this winter, where it started right up the last couple of winters. Once I do get it started, it idles at 1500-2000 RPM, often surging up to 2200 or so. I've found that when I move the shifter and hold it between park and reverse, it drops to normal idle. It does this warm or cold. Yesterday, something new happened. I went to start, and got the clicking, dead battery sound. Tach was bouncing around 300 RPM while cranking. I tried it again, but this time it started, but idled like crap, I got a CEL, and the tach went a little nutty. It sounded like it was idling at approx. 700-1000, and the tach showed that. If I touched the gas at all, the tach would jump to 4k and stay there until I took my foot off the gas. I didn't pull codes from the ECU, as it was butt cold the past couple of days. I turned it off, waited, started it back up, and it was fine. Hasn't done that since. Sorry for the long post, and thanks in advance for any help. I'm thinking maybe TPS. I'll grab a multimeter from work today and test that. BTW, I've been getting poor gas mileage this winter, too. ~17MPG versus ~22-23 average over summer.

 

The 4k is weird. Throttle flaps loose?
Others point to electricals, sensors & electronics.
Connectors cleanup, sensors tst etc: http://www.cardomain.com/memberpage/748507/14

 

Just to clarify, the revs would not jump to 4000, just the tach.

 

Then take a look at my web p. tacho scope pics BEFORE and AFTER connector cleaning, groundings... time for some connector archeology...

 

I don't think it was the guage connection that was the problem, as it only did this when the idle was horrible and the CEL was on.

 

I dont think either and did not say so: The gauge input comes (I suppose via ECU) from tachometer. Tacho gives out 1 & 120 degree pulses. If your connectors and/or distributor grounding, other groundings float, everythin happens. Like what u explain. Read carefully through, start cleaning from main ground under battery plate, go through all connectors, relays, ground points(and add some)...

Only after your harness neighborhood is in good condition, start digging error codes from ECU. Before that, pretty useless: carbage in, car bage out.