High RPM's on start up

[joshwilson3]

Do you have a matching graph for the temps the ECM is reporting? Trying to determine if the temp sensor the ECM monitors is working properly. You can measure resistance on the senor, but it is much easier using scanner data to see exactly what the ECM is seeing.

Here is the temp graph from the same scan as the RPM graph I posted:

And TPS to show the throttle isn't being engaged at start up:

I did try one test where after shut down. With Key "on". I grounded the ALDL which causes the IAC to extend all the way. Then I started the car up and still got the flare up. I was thinking maybe the IAC was being way to open on start up.

 

[TedC]

Nothing odd about those temp sensor readings. What's left? Vacuum leak, PROM or ECM? Did you ever pull the ECM to see what unit was installed along with the PROM identification information. If I remember correctly, we never verified that the PROM id was the correct one for your car. At a minimum, I would clean all the ECM contacts and related connector contacts. With BLMs on the higher side, how does it run at WOT? Would expect engine pinging. The ECM uses a preprogrammed enrichment mode at WOT.

 

[joshwilson3]

Nothing odd about those temp sensor readings. What's left? Vacuum leak, PROM or ECM? Did you ever pull the ECM to see what unit was installed along with the PROM identification information. If I remember correctly, we never verified that the PROM id was the correct one for your car. At a minimum, I would clean all the ECM contacts and related connector contacts. With BLMs on the higher side, how does it run at WOT? Would expect engine pinging. The ECM uses a preprogrammed enrichment mode at WOT.

I don't ever drive at WOT. I don't think I've ever smashed the gas pedal all the way to the floor. I guess I could a few times.

No I haven't pulled the ECM. That would be a pain anyways. Don't know if I want to do that. Nothing to indicate the PO replaced the chip. I don't think he did. Why are you thinking the PROM is wrong? That isn't something that normally gets changed. But I've had the car for years and didn't get a high RPM rev till just several months ago. So, I'd think if the PROM had something to do with it. Then I'd have a problem since I first got it, not years later.

I've still got some other checks to do like put the old O2 sensor back in. And disconnect the air tubes from the manifold air pump check valves.

 

[vetteboy86]

It appears that the tps voltage is jumping at the same time interval of the high rpm spikes. The scale is different but they do occur in the same area. The .2 volt change in tps would definitely increase engine RPM's.

 

[vetteboy86]

I'm looking at some of my scans and areas that the TPS voltage is .86 volts my RMP's are 1750 ish. This was cruising

 

[TedC]

Did you flip the throttle during this run that caused the TPS voltage spikes? During the first RPM spike, the TPS voltage did not spike. If the PO installed the wrong fuel rate injectors, who knows what else they played with. Just like you found the min air speed out of specification. This setting gets out of spec because owner lack the proper understanding of how a TPI actually works. Worked on a 1987 L98 that hesitated/stalled in open loop and pinged in WOT. BLMs showing a lean condition. Half way into checking over the engine we decided to pull the ECM and found a non-stock prom. Once the prom was reprogrammed back to stock settings the L98 ran great.

 

[joshwilson3]

Did you flip the throttle during this run that caused the TPS voltage spikes? During the first RPM spike, the TPS voltage did not spike. If the PO installed the wrong fuel rate injectors, who knows what else they played with. Just like you found the min air speed out of specification. This setting gets out of spec because owner lack the proper understanding of how a TPI actually works. Worked on a 1987 L98 that hesitated/stalled in open loop and pinged in WOT. BLMs showing a lean condition. Half way into checking over the engine we decided to pull the ECM and found a non-stock prom. Once the prom was reprogrammed back to stock settings the L98 ran great.

There wasn't any TPS spikes. I just posted the TPS scan to show the initial RPM spike on start up wasn't caused by the throttle being engaged. It looks like it is one of those weird things that you never figure out since it doesn't appear to be a common problem at all.

I'm going to install an adjustable FPR to raise the fuel pressure to get my BLM's and Integer closer to 128.

I also noticed getting some knock counts sometimes on my scans from part throttle under load. I found I couldn't pull a vacuum on the EGR. So, I'm going to replace that and hope it fixes the knock counts.