Won't idle up for cold start.
 

Hey guys, im having a really strange issue where my sc400 will not do the cold start idle up procedure. It just starts and goes directly to 600-700 rpm and sits there. Then the idle progressively gets higher as it warms up until about 1000 rpm then it sits there. Im at a complete loss and am starting to suspect a faulty ecu. Car is a 94 with 98k miles. It also had other random issues pop up such as trac light and for a while it wouldn't warm up but I just replaced the thermostat and it warmed up to operating temp finally, im just wanting to see if it holds temp at highway speeds, the oem seal for the thermostat blew out so it was never really closing fully. I have recalibrated the tps, cleaned the iacv(that got rid of my 1000-2000 rpm idle surge), distributor caps and rotors, plugs, and cracked open the ecu to find a leaking cap. Im lost but have a feeling its the ecu. First time I installed the iacv it started 3 times then wouldn't start unless I gave it gas, 2nd time I installed it it idled way high, 3rd time it idles fine but does not do the cold start sequence. Im getting horrid mpg (like 10) and i think thats because it was never warming up. It seems to me that the iacv isn't moving at all and I just have it in a spot where it will idle. The motor ohmed out fine with 43 ohms on each winding so I think the valve is fine. It spins free and I put a little lube on it to ensure that. No cel, and a very slight stumble at idle. You can hear it from the exhaust but only feel it a little. Has a slight bucking/surge at speeds. It also seems that the tranny shifts slow at wot. Thanks for the help!

If the ECU suffers a leaky capacitor, rebuild or replacement is necessary. Trying to get your car running right when it's running on a not fully operable ECU is going to go nowhere. Get the ECU rebuilt or replaced and then go from there. Tanin does great work. I had them rebuild my ECU and they did an excellent job.

Tanin all but refused to rebuild the ecu, they said it was not necessary. Im pretty sure this is my issue. Ive rebuilt both of my bmws so I know my way around, just new to this Japanese stuff. The link they sent me to get the service invoice was broken as well, they have not contacted me further.

Try the coolant temperature sensor it is the onnly sensor that tells the ECU what temperature the car is at. also check IACV wires