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Discussion Starter · #1 ·
I've been having idle problems for a while now. Initially, it would only happen when the car was hot. When I would get off the gas, the revs would hang at about 1800 and stay there until I gave the throttle a blip, then it would settle down to normal. The problem kept getting worse (happening in more situations) and also the normal idle got faster (indicating 1000-1100). Eventually the engine light came on for an idle control error.

I took it to a shop and they told me the idle air control valve was bad. I replaced it, but it didn't fix the problem.

I took the throttle body off and after close examination, I believe I've found the problem. The throttle plate is worn a bit on the cable side, creating a flat spot at the 9 o'clock position. This is causing two problems: 1) The flat creates a gap where excess air can get past the plate causing the elevated normal idle and 2) the flat causes excessive drag between the throttle body bore and the plate which leads to it getting hung up in a very slightly open position.

After playing with it some, it looks like the wear was caused by the return spring biasing the plate to the cable side of the throttle body. The friction between the body and the plate caused the flat spot to develop.

Has anyone ever seen this before? I'm having a hard time coming up with something that would cause this to happen on my car and not all of them.

I'm not sure what to do to fix it. A new TB from Toyota is over $800. The plate cannot be bought alone. I could get a used TB and swap the plates, but there's no guarantee that the one I get won't have the same problem. Plus I tried to take my plate out but the screws must be permanently loctited 'cause they wouldn't budge. Some heat might solve that problem, though. I could also have a new plate fabricated, but that might be tough to get just right. Of course none of these solutions would prevent the problem from coming back. I've also tried attaching a tension spring to the cable pully that both gives it a little extra closing force and also pulls the plate back to center. So far that hasn't worked, though I'm still playing with it. Finally, theres the Blackwatch big bore TB for $500, but that's a lot of dough and I'd be worried that when I supercharge it would cause a reflash tune to not work out so great.

Any other ideas?

Thanks a million,
Tom
 

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engine light

I experienced something similar last week. After a 1 week layoff, my engine lost power around 4,000 rpm a couple of times. Then, the engine light went on.

I took it to the dealer under the warranty. They "cleaned out" the throttle and installed "new software". I picked it up Friday, and the Lotus runs better than new.

I hope that this helps. I would add that it took about a day to diagnose the problem. Glad it was warranty work.
 

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Discussion Starter · #3 ·
Hmmm...I wonder if there was a problem with early ecu software. Unfortunately for me, the nearest Lotus dealership with which I don't have a contentious relationship is about 4 hours away. Still, I'm sure I have a mechanical problem, so I don't think a software update would be a cure-all for me. Glad yours is working out, though!

Oh yeah, and the shop that misdignosed the IAC valve took 4 hours to arrive at that conclusion. Wish that was under warranty...

Tom
 

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what year cars are these?
Seeing as he is referring to a return spring, IAC valve, and a cable, I assume this is an '05.

If I am wrong and he is talking about the TBW throttle body for the later cars, I have one in perfect condition (1,100 miles) from an '06 I would be willing to sell for much less than $800.
 

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To me this sounds like a perfectly valid excuse for the BWR throttlebody:shrug:

Could likely take the plate out and have another one made....but w/o the flat spot. Those screws are in there pretty well. have to make sure you have a good driver, a vise, and don't slip.

I'm curious as to how that flat spot got there. makes very little sense to me, as I've never seen a TB "wear out" like that.

Pics?

If you can get it apart, might try smoothing things out a bit. if its all smooth it won't hang up. and in reality what the worst that you can do? (if it works great, if not you're in the same boat as right now.)
 

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Discussion Starter · #8 ·
BWR is definitely an option, but it would dip into my SC fund. Also, what are the chances that the BWR TB would screw up a reflash tune? My last bout with the added tension spring looks like it might be doing the trick...need to put some more miles on it.

I have no idea why my car developed a flat spot and none others seem to be. If I pull the TB off again, I'll snap a pic.

Have you taken the plate out? Are the screws just permanent loctited, or did they swage them or something like that?

Thanks,
Tom
 

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BWR is definitely an option, but it would dip into my SC fund. Also, what are the chances that the BWR TB would screw up a reflash tune? My last bout with the added tension spring looks like it might be doing the trick...need to put some more miles on it.

I have no idea why my car developed a flat spot and none others seem to be. If I pull the TB off again, I'll snap a pic.

Have you taken the plate out? Are the screws just permanent loctited, or did they swage them or something like that?

Thanks,
Tom
I haven't taken the plate out on a Lotus. I did it on a Mustang, also had a buddy who was boring out LS TB's. They seemed to have a clear loctite stuff on them. hard to break loose, but once broke they came right out.

Have you looked at another one to make sure this flat spot is "wear" instead of intentional for idle? I'm just thinking outloud. If I could I'd yank mine off and look @ it. but its kinda a PITA on this car.

I know some have holes, some have machined gap, and some just keep the flap slightly open when its "closed" to maintain idle.

Also if you yank it off again you might be able to hold the flap completely open, and buff out the rough edges. Makes me wonder...maybe machining nonsense?
 

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Discussion Starter · #10 ·
Gotcha. I don't think it was put there on purpose since depending on how I bias the shaft left-to-right the gap either goes away or becomes pretty big. If it were round it would self-center. I think the idle air control valve eliminates the need for a significant hole. I will definitely give it a nice polishing if it comes out again.

Thanks!
 
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