Fast idle when hot

[Dave Ledwitch]

Recently I have had an issue with idle when up to temperature.

From cold everything is fine.

I can watch the rpm & IAC reduce steadily down to 1070rpm.

When i drive though. there is an rpm increase on gear change and idle settles at around 2000 rpm.

even though the Throttle position is zero.

I have recently done the following:

Upgraded chip to #10

fitted recirc dump valve

taken up some slack in accelerator cable (still loose at rest)

In an attempt to fix this I have reset the BLM, reset the IAC, taken off the TPS and reset.

Still no improvement.

According to the manual, high idle is likely to be a vacuum leak.

But from where and how can i test this?

Any thoughts or suggestions welcome.

Attached is a freescan file.

Dave

idle_5_5_08.csv

[esprits4de]

EBPV and so forth... read up at LEW tech section......

[Dave Ledwitch]

Thanks for your suggestion Olaf.

I dont think my GT3 has a EBPV though.

I will return the car back to std i think and fix it from there if the problem still exists.

Embarrisingly I have broken the throttle cable adjuster and have locked it in one position. Is there any throttle cable adjustment potenital at the pedal end?

Dave

[Bibs]

I'm not expert Dave but your freescan log looks fine to me, the TPS is a tiny bit low (0.57, should be 0.6 to 0.66) but other than that I can't tell if anything is wrong from it.

I had the same problem, did a proper ECU reset and it's cured for now, have you tried that?

[Dave Ledwitch]

Thanks Bibs.

I did do an ECU reset when i put the new chip in.

Got a backfire on first attempt to start!

I am thinking that the the accel cable may be getting tight as the engine gets up to temperature so I will slacken it off properly first.

Dave

[Dave Ledwitch]

I had another look at the freescan file and noticed that the numbers in the BLM cell column change.

When I get 19, the idle is ok.

With BLM at 1, I get 2000rpm

With BLM at 4, I get 1500rpm.

I also got readings of 8 & 9.

All i did to promote the change was to blip the throttle.

I have reset the IAC and ECM again and now get BLM cell readings of 19 (ok) and 4 (1500rpm)

Does anyone know what determines the BLM cell contents?

When I changed the chip, i didnt solder the carrier in. Could this be the result of intermittent chip connections? I cant find any vacuum leaks, which would be the obvious answer.

Dave

[Bibs]

Dermot is the man to help here, he knows more about Freescan and our ECU than anyone!

[98GT3]

I had another look at the freescan file and noticed that the numbers in the BLM cell column change.

When I get 19, the idle is ok.

With BLM at 1, I get 2000rpm

With BLM at 4, I get 1500rpm.

I also got readings of 8 & 9.

All i did to promote the change was to blip the throttle.

I have reset the IAC and ECM again and now get BLM cell readings of 19 (ok) and 4 (1500rpm)

Does anyone know what determines the BLM cell contents?

When I changed the chip, i didnt solder the carrier in. Could this be the result of intermittent chip connections? I cant find any vacuum leaks, which would be the obvious answer.

Dave

Hi Dave,

I would suspect a bad chip connection - the socket for the EPROM should always be soldered in!

If you look at your numbers and think of them made up of binary 1,2,4,8 etc, then you only need one pin without connection and you will miss large chunks of data stored in it.

Phil

98GT3

[Vulcan Grey]

The throttle cable getting stretched when the engine grows is very possible in these cars. I've adjusted a throttle cable on an 89 and then had a very fast idle once the engine warmed up. I re-adjusted the throttle cable with alot of slack when the engine was cold, and it still stretched enough to pull high rpms when warm. Finally I adjusted the cable when the engine was hot, and it was fine after that.

Also the Throttle jack can get sticky (even if it is disabled) and the linkage can cause the throttle to stay open a bit.

[Dave Ledwitch]

I have now checked the accel cable. slack when hot.

I looked at the memcal today and the chip was loose in the holder. Pushed it back in firmly, reset IAC but the problem is still there (when i saw the loose chip I was sure this was the cause).

I will focus on the IAC next.

Dave

[Dermot]

Dave,

It was unlikely to be the memcal or loose chip. The ECu does a checksum check on the EPROM at startup and if it is incorrect you will get a check engine light (CEL) and the fans will come on.

a mechanical problem like a tight accel cable would do it as the ECU is struggling to drop your revs. Also there is a hunting pattern to the rpms.

I would give the IAC a detailed check.

[waynef]

Had the same problem with mine a while ago. It would run fine some days and then others it would run at 1500 -2000 rpm.

Sometimes it would be fine and then when I pulled up to a juction it would do it.

I tried everything and in the end it turned out to be a vacuum leak.

The rubber hoses in my S4 are practically 14 years old and perished, so I replaced the lot with silicon hoses.

Problem sorted straight away.

Funnily enough the other day I was playing about with the stereo out and the problem came back. What I did not realise was that i'd disturbed another vacuum pipe when I placed the stereo back in. Symptoms were again fast intermittent idle.

My money is on you have a vacuum issue.

Easy check is to turn your ignition on and wait to see if the buzzing noise from the engine bay stops if it does then fine but if it stops and then starts then stops and starts and so on you have a tiny leak.

Waynef

[fflyingdog]

My vac motor buzzed continously until i fixed my fresh air flap actuator,and to be honest it had no effect what so ever on my idle speed,if mine does climb at engine start i just "stab" the throttle and it drops to normal idle speed.Also reading back through your post ,you said car idles normaly when cold ,i think the vac leak would manifest itself alot more from cold ,is your rpm constant when hot? (apart from being too high) no spluttering or hisses or hunting?

Cheers

Nick S4s

Edited May 18, 2008 by fflyingdog

[Dave Ledwitch]

Vac motor buzzes and stops.

If it cuts in again it is not for a while, maybe after 30 seconds for a short period.

I have a vacuum pump & gauge so will check vac hoses with that.

The fast Idle is not stable but does not splutter or hiss.

In the meantime I have ordered a new IAC.

Should be fitted for Castle Combe this weekend.

Dave

[Dave Ledwitch]

So I replaced the IAC and....... Still the same!

Idle from cold comes down to 1070 fine but when hot hovers between 1500 & 2000rpm!

I decided the next thing was to look for a vacuum leak.

As I have recently fitted a dump valve and replaced the existing vac hose with silicone i thought I should check here first.

I fitted the original vac hose and bingo! hot Idle is back to normal!

So there is a leak in one of the silicone hoses or the dump valve itself.

Will investigate further and let you know what i find.

Well done Wayne. Seems to be a vacuum leak.

Dave

[superdavelotus]

Hi Dave,

To rule out dump valve and connection, take the vac line off and reconnect your vac line as though you haven't got a dump valve. A simple 5 min job will determine whether it's the dump valve vac line leaking or not.

If it's not this then look at your throttle jack and vac line connections. It's on the front of the engine on an aluminium bracket. It's a very crude solenoid which pushes the lever on the throttle. If the bracket is bent or there is a problem with the throttle jack or signal to it then it could be forcing the revs up!

Regards,

Dave Walters

[Bibs]

I'm struggling with this too, my TPS voltage is now fine but when the car is warm it's reading 10% which I'm guessing is down to the throttle cable as my EBPV is removed and throttle jack are disconnected.

Is adjusting the throttle cable an easy job, can I do it? It's pretty slack cold and although I'm getting 100% throttle, it could do with the slack being taken out.

[Dave Ledwitch]

Bibs

Be careful with the throttle adjuster at the engine end. All too easy to overtighten and break it!!!

I have noticed there are adjustable stops for the accelerator pedal movement.

you can use these also to remove slack in the cable.

Dave

[Kimbers]

Lotus replaced all my sensors, exhaust valve etc and it worked fine for 2 weeks and now it's back to 2000 revs when hot as well.

I've just given up. Least it stops me stalling!

[superdavelotus]

Can't you reset your idle on freescan when engine is warm?

Dave

[Bibs]

The voltage would be too low when cold and chuck a CEL.

[Dave Ledwitch]

I have success!!!

Hot idle back to normal.

I find it difficult to believe but when the engine is hot the new silicone vacuum hose leaks on the intake manifold connection.

I have swapped out the silicone hose for smaller diameter vac line and fitted small spring clamps to all of the joints.

I am amazed that such a small leak would have such a big effect!

Just in time for Castle Combe.

See you there.

Dave

[waynef]

See you should listen to good old waynef

BAck to basics, remember the Esprit Engine is very basic

Told ya Lol

Waynef

Edited May 24, 2008 by waynef

[Dave Ledwitch]

AARRGGH!

Idle is still fast, despite a brief period where i thought it was fixed.

I have started to get error codes now.

22 & 34.

For 22, TPS, I ran freescan at idle again and got 0.45V but TPS of 5%, even though the accel cable is slack. How can that be? I thought there was a dead zone, 0%TPS until 0.7V?

Is the sensor faulty or the ECU?

Does anyone know how to check?

For 34, MAP, as I have a GT3 this is located by the ECU. It is not as described in the manual I have, it only has 2 spade connectors. Freescan Sensor diagnostics gives 2.35V and 0.9 bar but no change when I apply vacuum or pressure. I cant measure any voltage or resistance accross the connections at all.

Does anyone know how this should work and how to test it? How can freescan measure 2.35V but not my voltmeter?

BTW I also looked at the Baro Pressure sensor and this is working but giving low voltage according to the manual. Manual says it should give 4.8V but is giving only half of this despite baro reading 0.9 bar. Testing with vacuum as per the manual gives half voltage readings. Did Lotus change this sensor post 96?

Regards

Dave

[Dave Ledwitch]

For 34, MAP, as I have a GT3 this is located by the ECU. It is not as described in the manual I have, it only has 2 spade connectors. Freescan Sensor diagnostics gives 2.35V and 0.9 bar but no change when I apply vacuum or pressure. I cant measure any voltage or resistance accross the connections at all.

Does anyone know how this should work and how to test it? How can freescan measure 2.35V but not my voltmeter?

Please disregard this bit. I was looking at the Boost gauge transducer . DOH!

I have found the real MAP sensor now...

Dave