inconsistent idle and lurching at constant speed

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inconsistent idle and lurching at constant speed

Postby GreasyJoe » Sat 14.01.2023, 18:18

Hi all, I'm after some guidance on where to start looking.

Firstly inconsistent idle on occasions. Normally the car will behave itself sitting nice and evenly on tick over but other times, either initially starting the car or a little time down the road, I can get either idle bobbing quickly around 950 and just below. Other times the engine will idle at about 1500 or on the very odd occasion near 2000 rpm, like its still compensating for being cold, though its just about warm? Eventually it may settle but not always. Sometime turning the engine off resets things?

The other issue I've noticed is the car is going along at constant 30mph not under acceleration, and will noticeably lurch/jerk a few times, then continues normally,
The engine temp can be from cold to running temp (though the gauge in the car hardly moves to near quarter unless in last summer stuck in traffic). Though less likely to do it when up to full running temp.

The car can behave itself completely on other occasions. It can be quite random.

It has a new air filter
Haven't changed the fuel filter or plugs so not sure how old they are. Though as said when it runs and accelerates it seems fine.

Any suggestions what is the cause, where to start looking? (Order by obvious to the obscure please)
Any sensors/electronics that could be playing up?
If suggests vacuum hoses leaking can someone point me where they are and the diameter inner/outer size and length of the hoses I'd need to replace, as not been able so far to find any details.

Owned the car for nearly a year. Was previously SOARN for a couple of years before and got MOT'd prior to putting it up for sale. Was serviced but not really maintained for its age.

The car is 1992 SE turbo, approx. 85k miles (under restoration when the weather gets better. Most rubber items may need replacing hence the mention of the vacuum hoses).

If you want to see the car, it was used to review the model on youtube the other year. Not sure why he picked mine as a 'good' example? lol

[url=https://www.youtube.com/watch?v=EaaopxfJMu4&t=98s]
Last edited by GreasyJoe on Sun 15.01.2023, 03:01, edited 1 time in total.
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Re: inconsistent idle and lurching at constant speed

Postby texas2201 » Sat 14.01.2023, 19:52

I've got a similar problem..... well the lurching/stalling bit .... I'm still trying to solve it - I do one thing and it gets better - then it comes back...... going into garage for a smoke test for vacuum leaks and to check the base timing. Now it seems to be over fuelling - flooding - so suspecting one of the injectors is sticking - so they will get checked as well

i've fitted new plugs, coils, VSS, throttle cable, injectors,
"brakes are no good - they just slow you down" Fangio :-)
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Re: inconsistent idle and lurching at constant speed

Postby GreasyJoe » Sun 15.01.2023, 03:00

texas2201 wrote:I've got a similar problem..... well the lurching/stalling bit .... I'm still trying to solve it - I do one thing and it gets better - then it comes back...... going into garage for a smoke test for vacuum leaks and to check the base timing. Now it seems to be over fuelling - flooding - so suspecting one of the injectors is sticking - so they will get checked as well

i've fitted new plugs, coils, VSS, throttle cable, injectors,


Interesting you mentioned overfuelling. have had a smell of petrol since i got the car. never sure where it is coming from. a lotus specialist didn't pick anything up. not sure if its around the tank or the engine. never really noticed it in the engine bay though always thought the exhaust was a bit sooty (not sweep ;) Just another thing to investigate.
Strange you mention you replaced the injectors but you think it may still be one sticking?
Be good to know how you get on texas2201
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Re: inconsistent idle and lurching at constant speed

Postby texas2201 » Sun 15.01.2023, 10:46

Will do.... see what Tuesday results in
"brakes are no good - they just slow you down" Fangio :-)
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Re: inconsistent idle and lurching at constant speed

Postby texas2201 » Sun 29.01.2023, 12:40

Garage was very helpful - but it was out of their depth. Did find that the new VSS was loose ..... removed, refitted and tightened. No change to the problem.

Piggy backed a new Temp Sensor and as soon as engine was warm EML came on with a code 21 TPS ..... seems like the bad CTS was "hiding" this before.

Ordered a new TPS from Rockauto and a proper CTS - allegedly arriving Wednesday .... in Portugal from the US ..... we will see

And of course one of the screws on the TPS has been mullered by a previous visitor!!!! New screws and Throttle body gasket (the one fitted is in perfect shape/condition) will be ordered from SJS if the transport price is not offensive. Lost a jubilee clip in the engine bay - will keep looking for it. Bottom hose on TB was spawn of the Devil snap on Clip..... I F**kin hate those - came off in two pieces.... 40 mins of my life I wont get back!!!! so another Jubilee needed.
"brakes are no good - they just slow you down" Fangio :-)
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Re: inconsistent idle and lurching at constant speed

Postby dapinky » Sun 29.01.2023, 12:55

Martin,

When I changed the TPS on the old red car, the screws were bu66ered - they are a simple M4 setscrew (I cant remember if they were M4, or M5 - but they are a standard thread which I had in a box!), so i just replaced them with 'normal' hex-head ones from the garage shelf and used a small spanner to nip them up.
Dave

Just the one now, but this one's mine! - and it will be finished eventually..... - but also temporary custodian of a project until it is finished enough for Angie to drive it

go on - click this link - you know you want to!
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Re: inconsistent idle and lurching at constant speed

Postby texas2201 » Sun 29.01.2023, 13:38

dapinky wrote:Martin,

When I changed the TPS on the old red car, the screws were bu66ered - they are a simple M4 setscrew (I cant remember if they were M4, or M5 - but they are a standard thread which I had in a box!), so i just replaced them with 'normal' hex-head ones from the garage shelf and used a small spanner to nip them up.


thanks Dave
"brakes are no good - they just slow you down" Fangio :-)
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