On a hot start car will immediately rev to 3500 rpms for 15 secs, then settle back??

[Jeffu]

For the last 3 weeks I have noticed the motor wants to rev up to 3500 RPM for approx 15 secs when the engine is re-started (only on a "hot" motor). After the 15 sec or so, the engine falls back down to a normal idle. Any ideas?? This appears to be happening only when the car has reached normal operating temp or is good and warmed up. If I have been driving the car around and let it sit for 20 - 30 mins then try and start, I don't have the issue. On the flip side, the cold start idle and all other idles conditions are fine. Anyone able to offer any insight?? thanks!

[Bitsyncmaster]

Not a common fault to idle that high on a warmed up engine.

Could be a lot of things but most problems with our cars are bad connections. I would unplug and plug back in the connectors on the bulkhead and idle ECU.

[opethmike]

Not a common fault to idle that high on a warmed up engine.

Could be a lot of things but most problems with our cars are bad connections. I would unplug and plug back in the connectors on the bulkhead and idle ECU.

+1

Clean up the connectors while you have them apart too. Amazing how nasty they can get.

[Jeffu]

Thanks you guys! Yes, I completely went through my bulkhead connectors last year and cleaned and repaired many of them. I am pretty confident they are "OK", (knock on wood of course). I just now pulled the two plugs on the ECU and looked at them. They do not appear bad or really oxidized. However, I shot some electrical cleaner on them anyway. I am going to take it out for a spin and see what happens. I will keep you posted.

[Jeffu]

Well, cleaning the terminals on the ECU did not seem to make any difference. It is definitely something electrical because (well obviously) there is no mechanical movement of the throttle cable/linkage etc when this occurs.
**correction **
This issue seems to only occur within approx 10 mins or less of re-starting the warmed up motor. Outside of this time frame (10-11 mins or longer) there is no issue. This also leads me to believe it is temp related as well, ie: expanding or contracting of electrical components??
Strange things indeed.....:hmm:

[Bitsyncmaster]

If you know another owner, try to borrow his idle ECU and test it in your car. It does sound like an electronic component failure since it's so repeatable.

[Jeffu]

I sure wish I could find someone over here in Boise, ID! I have had a few people stop me and get my info claiming they have relatives or friends with "D's" but I have never heard from anyone yet.
However, I am traveling to WA this coming weekend for a Delorean function and I will be able to use/test 2 different ECU's from my buddies cars. I will see what happens.

[Renee_1632]

I think the engine IS supposed to rev somewhat....mine usually revs up to 2000 then settled back. Never 3500 though.

[Henrik]

I am having the exact same problem. Here is what I was told over at dmchelp.com (but I haven't looked into it yet):

Probably a sticky idle motor but could be the idle ECU. I think the norm is about 1500 RPM starting and quickly drops (one second or less) to 775 RPM.

I would suggest you remove the idle motor and clean it with solvent (the valve area). Do not use any metal pokers to rotate the valve. Use a wooden stick. Then I use a lot of "3 in 1" oil in the valve and let it drain a few hours on it's side. A few drops on the upper bearing is also a good thing but you have to remove the threaded plug to do that.

[Jeffu]

Can't believe it took me this long to get back to this thread.

So here is what I found out. It WAS the ECU. I had cleaned all of the connections, cleaned out the Idle Speed Motor and had no change. Next, I had a buddy of mine send me an ECU out of one of his cars. I popped it in and started it up and immediately I could tell the engine idled a bit better. The hot engine issue of revving up to 3500 rpms on the restart is completely gone! Now, immediately upon a warm/hot restart the engine rpms gently raise to approximately 2000 for a couple of seconds, then settle down comfortably to around 750 rpms.

[David T]

It could still be a bad connection somewhere, your ECU is just more sensitive to it. Rare to see an idle ECU malfunction. Just the act of plugging and unplugging things can sometimes "fix" things and you think it is the "new" part!
David Teitelbaum

[Bitsyncmaster]

It could still be a bad connection somewhere, your ECU is just more sensitive to it. Rare to see an idle ECU malfunction. Just the act of plugging and unplugging things can sometimes "fix" things and you think it is the "new" part!
David Teitelbaum

This is so true. I have seen a few ECUs go bad but that was blown output transistors. So there was no idle control at all with those bad units.

[Jeffu]

Previously I had unplugged and re-plugged my old ECU about 5 different times. I also made sure that my connections were sound and tight. That did not make any difference.

So today, just for fun and giggles, I unplugged the replacement ECU that I had received from my buddy and put my old one back in. The same old problem replicated itself once again. So, I pulled my old unit and put back in my buddy's unit and it seemed to correct the issue once again.

I am no electrical engineer by any means, but it just seems to me that my old ECU has some sort of issue.

[Bitsyncmaster]

Previously I had unplugged and re-plugged my old ECU about 5 different times. I also made sure that my connections were sound and tight. That did not make any difference.

So today, just for fun and giggles, I unplugged the replacement ECU that I had received from my buddy and put my old one back in. The same old problem replicated itself once again. So, I pulled my old unit and put back in my buddy's unit and it seemed to correct the issue once again.

I am no electrical engineer by any means, but it just seems to me that my old ECU has some sort of issue.

That sure sounds like a good test to prove your ECU is bad. Good work.

[David T]

As a final confirmation you should try the suspected faulty ECU on another known, well functioning, Delorean. I have seen many times some parts are just sensitive and while they won't work on one car they seem to work just fine on another.
David Teitelbaum