1997 mystery cold start issue (1 Viewer)

[OOCustoms]

Ok- here’s the deal. When the truck is cold started, it fires right up- idle is around 1000. Within about 45-60 seconds it starts to shudder, idle drops very low, engine surges and stumbles for about 60 seconds or so- sometimes stalls, sometimes comes out of it and suddenly smooths right out. If it stalls, it will fire right up again, shudder for a few seconds, then recover. (It does have a bit of a lag with the throttle but not too bad.) The truck can be driven after about 2 minutes with no issues. It can be shut off, restarted with no issues while still warm-ish. The cap, rotor, plugs, plug wires, IAC sensor, temperature sensors, oil pump, TPS, O2 sensor, knock sensor have all been replaced. New computer. Compression is good. Any ideas?

 

[Malleus]

Idle air control valve. Take it off the throttle body, disasssemble it, clean it, reinstall it. The two functional tests are in the engine section of the FSM.

Unless it's been removed recently (w/in the last couple of years) it's best to remove the throttle body to get it off, as the small JIS cross point screws will likely be stuck and you need leverage to get them off, especially the lower one which is nearly unreachable when the TB is on the intake.

If it fails the functional tests, either one, and you can't restore it by cleaning it, '95-'97 types are still available new.

 

[OOCustoms]

IAC is new- I guess I can test it to make sure resistance is correct, but chances I got a bad one are slim.

 

[ajax1]

Check engine coolant temp sensor not the one for the gauge, but for the ecu. Lives on the left hand side of the engine head, there will be three sensors I think without looking it up it is the first one closes to the front of the engine

 

[OOCustoms]

All the sensors that the ECU uses are new- however I think I might have found where my issue lies- I tested the IAC harness for resistance- (3-10 ohms) and it's way out of spec. Looks like I have a short somewhere in the harness between the connector and ecu. ****.

 

[fjbj40]

All the sensors that the ECU uses are new- however I think I might have found where my issue lies- I tested the IAC harness for resistance- (3-10 ohms) and it's way out of spec. Looks like I have a short somewhere in the harness between the connector and ecu. f***.

Find the problem?

 

[OOCustoms]

No- still looking. harness turned out to be ok.