Harsh start and high idle at startup

[jigz]

2000 Holden VX.

By harsh start I mean, it seems aggressive. Rarely, a check engine light will come on, and it won't start, but 99% of the time it starts fine, just a bit harsh, like almost a clunk at times. Brand new Bosch starter motor.

Then, it revs up to about 2000, stays there for what seems like a few minutes, then drops back down to 1000 at idle. Mostly, it does this first start of the day, then it's fine. Sometimes it does it throughout the day, multiple times. I've read that it's normal for it to rev high initially at startup? But every time? It doesn't seem like it would be good for the engine to be revving at 2000 straight off the bat?

I'm thinking it could have something to do with the IAC valve (new), EGR valve (new) - does EGR valve need calibrating? Also, one of the wires that links the DFI module with the IAC was burnt out at the pin on the DFI module, cleaned up and fixed, will check how that's going. Suggesting to me something electrical?

Any ideas?

Hope I've provided enough info.

 

[commodoredave]

2000 Holden VX.

By harsh start I mean, it seems aggressive. Rarely, a check engine light will come on, and it won't start, but 99% of the time it starts fine, just a bit harsh, like almost a clunk at times. Brand new Bosch starter motor.

Then, it revs up to about 2000, stays there for what seems like a few minutes, then drops back down to 1000 at idle. Mostly, it does this first start of the day, then it's fine. Sometimes it does it throughout the day, multiple times. I've read that it's normal for it to rev high initially at startup? But every time? It doesn't seem like it would be good for the engine to be revving at 2000 straight off the bat?

I'm thinking it could have something to do with the IAC valve (new), EGR valve (new) - does EGR valve need calibrating? Also, one of the wires that links the DFI module with the IAC was burnt out at the pin on the DFI module, cleaned up and fixed, will check how that's going. Suggesting to me something electrical?

Any ideas?

Hope I've provided enough info.

If you have a fault code reader check the fault codes. Aside from that try disconnecting the battery for a few minutes. This will reset the PCM. to eliminate possible faults step by step/. If you still have the old IAC etc try installing them one at a timer to isolate the fault. Its laborious and epic but in absence of better options give it a try.

 

[Pollushon]

Assuming an Eco, you can bridge pin 5 and 6 on the ALDL interface port (from top left), turn the key to reds and the CEL will flash you the codes. If you have ever had a CEL then you have a great place to start before you replace the engine piece by piece with hope as your strategy

Could be a bunch of things causing the issue, agreed it's likely in the IAC space or a vacuum leak

 

[jigz]

The codes I pulled by bridging pins 5 and 6 were:

0506 - Idle Control System RPM lower than expected
1361 - Top Dead Center sensor

The crank angle sensor has only been recently replaced