limon32

So i've got an issue with a 1990 pickup, 5-speed, 3.0

When the engine is cold, it starts ok, sometimes takes a few seconds of cranking and a step on the gas pedal to get started. Idles fine when cold, but if you try and drive it while cold, it stumbles with a normal amount of throttle and release of the clutch. To get it to go you have to rev the engine pretty high. Once it is warm, it has normal take off and doesn't stumble, but it has a loping idle.

I have checked the following items per the FSM:
TPS - ok
AFM - ok
Vaccum - no leaks, I did have a bad EGR modulator but thats fixed now.
Throttle body - I removed it, cleaned it put it back on.
Timing - checked multiple times
Wires, cap, rotor have been replaced, plugs look fine.

Next things I plan to check are:
Coolant temp sensor
Cold start injector

Any other ideas? I'm stumped!

93YotaMonster

is the check engine light on

limon32

No, sorry, should have added that. The CEL was on when I bought the truck but it had a generic O2 sensor on it so I replaced with the correct part and CEL went out. That was about 8 months ago.

93YotaMonster

well try to pull some codes and see if anything popes up

limon32

So there can be codes even if the CEL is not lit up? I guess I just assumed there wouldn't be codes if the CEL wasn't on... My bad, i'll do that ASAP! Thanks!

Brad.

Maybe a small vacumm leak somewhere?

limon32

I sure checked the piss out of the vacumm lines, I found the bad EGR modulator while doing the seafoam treatment and smoke came rolling out of teh EGR modulator. I suspect I would have found any other leaks at that time but maybe not. Short of replacing every vaccum line I sure can seem to find any more leaks.

I read something that made me think there may be vaccum lines to the steering pump or AC pump, if so I haven't checked those, any thoughts?

Brad.

There are I think two lines to the power steering pump, no reason they should be leaking unless they have been put on and off several times. Doesn't hurt to check them out though.

limon32

Will do, thanks!

limon32

Ok so I pulled codes 21, 24 and 41.

21 - O2 sensor
24 - Intake air temp sensor
41 - TPS

What are the chances of all three of these being bad? I'm starting to wonder if the ECM is bad?

limon32

Can anyone tell me where the intake air temp sensor is on the 3.0? I can't seem to find it!

limon32

Ok I just measured the cold start injector, coolant temp sensor and cold start injector timer and all resistances are within in spec. This isn't fun anymore...

I also pulled the electrical connection from the cold start injector and started the truck, it runs exactly the same way as when the injector is plugged in! I'm guessing this is not good? I'm thinking about replacing the cold start injector, timer and coolant temp sensor, anythoughts?

magnum

you don't really need the cold start injector, on my rig if its plugged in my truck wont even run. i just pump the pedal a whole lot before i try starting it on a cold day.