Runaway rpm at idle

[benfell100]

Well not quite runaway but when its idleing at 1800 it sounds a bit keen. Geoff said it could be either vacuum hoses bust/disconnected (I checked, can't see any but there may be a cracked one) or the TPS throttle position sensor is stuck.
Any ideas?
Looks like another little job for Geoff. Think I will get the throttle cable changed too as its frayed a little.
Dom

[adrianmugridge]

Dom

My GT3 did that, it's most annoying ! Does it reset if you cycle the ignition ?

I plugged freescan in and it said it was getting about 5% throttle input so that was causing the problem.

Adrian

[oharedm]

Adrian,

Could be that, throttle jack, IAC or TPS.

It woudl be useful to see what idle the ECU is demanding. Manifold leaks can be sometimes spotted in the Freescan log by looking at the MAP and Baro readings at idle.

As always can't help much more without a log file.

Dermot

[benfell100]

exactly my thoughts Dermot, I have the cable and program, just need a darn laptop to play it on...
started it up today and it didn't reproduce the fault, it idled normally. Bloody things...

[lotusespritworld]

Mines been doing the same on and off for a while now. Will idle at around 1800rpm even after a long motorway journey. Turn the ignition off and back on again and it drops back to 1100rpm. Comes back every now and then.

Haven't managed to get freescan running on it while it's doing it. Happens probably 1 in 5 times I use it.

kato
Lotus Esprit World

[benfell100]

Interesting Kato. It idled perfectly when I took it out the garage, I let it warm up till the fans cut in, the vaccum pump worked fine, couldn't find any leaking or detached vacuum pipes etc so I assume it is a dicky electrical switch like the TPS or somesuch. Hopefully Geoff will plug in freescan when the car is at 1800 rpm after I take it down and he should be able to get a better idea. Won't be there for another week or so though
Dom

[lotusespritworld]

Any update. Mines still doing it occasionally.

kato
Lotus Esprit World

[igreenrover]

Hi all

Mine has been doing it for over 12 months now. Did try and get some help through the forum last summer but no luck. I still have the file though that shows a change in the idle RPM, I’ll see if I can find it.

I've changed the TPS,IAC valve, vac hoses, ECM, Fuel PRV, and also the Pump.. still the same 'On and off'

Gareth

[cnh1990]

Mine did that when I used a different type of fuel. I had been using non OX then while low on fuel used an oxengenated type. I had to reset the ECU to make it idle right even after I switched back to non OX.

[deecee]

Sounds like there may not be enough slack in the Throttle Cable.

[igreenrover]

I found my full export from last summer. Its easy to see where there idle speed changed:

http://idisk.mac.com/garethspencer/Public/fulldata.xls

[superdave]

My S4s does it now and again when hot or hot starts. I have to quickly blip the throttle and it comes down again. It only takes a flick of the pedal nothing more.
As it not that bad, I have never looked into why it does this. Car goes on Monday, it would be nice to get to the bottom of the problem before then.



Dave Walters

[cross-eyed-twit]

Mine is fixed.
Geoff changed the thermostat, throttle cable which was old frayed and loose and it seems to have fixed it. The throttle response is now instant and I admit I Kangaroo'd off from the workshop after picking it up as I wasn't used to it :-)

May be worth a new cable (£?) and t'stat (about £8.00) as these are inexpensive I think.

I think thats all he did but email him and refer to my problem if unsure.

Dom Benfell

[lotusespritworld]

blipping the throttle doesn't reduce my idle. I have to turn the ignition off and start it up again. Then it always returns to about 1100rpm. Got to be something to do with the auto-choke. It only happens from cold.

Then engine revs at 2000rpm on cold start and drops to around 1000rpm after a couple of minutes when working properly. When it's playing up it will stay at 2000rpm. I've even come back on a long journey and pulled off the motorway. dipped the clutch to stop and it's idling at 2000rpm. Switch it off and on and it's fine!

Anyone got any ideas. Only happens every now and then.

kato
Lotus Esprit World

[britten_mark]

I asked about this at the dealers last service, they said they all do it to some extent, not necassarily a problem. I told them it was a bit embarrassing sounding like a learner driver doing a 3-point turn, all they could do was agree.

[oharedm]

one source of fast idle, especially on warm strats is the throttle jack capsule. Total junk, throw it away and blank off the vacuum feed.


If you run freescan while it is doing this you can see what the ECU is trying to set the RPM too.


Dermot

[lotusespritworld]

LEW's Esprit is at Hethel at the moment and they are looking at the throttle 'hang up'. Currently they have replaced the IAC valve as a starting point. Hopefully they'll find a cure and I can post the details here.

kato
Lotus Esprit World

[igreenrover]

Kato, very interested to see what they find. As said, I'm at a total loss on this now.

Gareth

[princecharming]

I agree with Dee Cee. There might not be enough slack in the throttle cable.

Earlier this year, I took the slack out of my throttle cable, thinking that it would give me better throttle response. It was great when things were cold, but after driving her for a while, the idle gradually increased as the car got hotter. Eventually, it was up around 1600 to 1800RPM and higher. Drove me nuts since I knew it was shortening the life of the clutch every time I had to step on it to get home.

Checked the cable as this was occuring and discovered that the cable was pulling the throttle open when hot. Now this goes contrary to everything I've always believed since I thought metal expands rather than contracts when hot, but sure enough, it happened every time the car was hot until I put a little more slack into the cable.

Once I did that, the problem never recurred. Also, on my car, it couldn't have been the throttle jack since the PO removed it. Couldn't hurt to take a look and see if you need a touch more slack.

[princecharming]

Oops, just realized that Cross-Eyed-Twit is the same as Benfell and that the problem was solved. Sorry 'bout that. Please disregard my previous posting. In the case of mine, re-starting the engine did not improve matters since it was the cable.