Lotus Elise SC Throttle Problem

406 Views 11 Replies 3 Participants Last post by Catsailr27, 12 d ago

MikeNa

Discussion Starter · 13 d ago

Hi guys,

I've got a throttle problem with my Lotus SC. Whenever I stab/blip the throttle quickly (Rev matching/shifting quickly) the engine would cut off like it's running out of fuel. After releasing the throttle, it would return to normal.
Redlining, idle, part throttle are all perfect.

I've replaced/checked most of the obvious such as new spark plug, reset ecu, vacuum routing, ecu wires intact, etc

Finally when I was taking off the TB to check and clean, I realized that it's making buzzing and crackling noise.
TB Crackling Noise

Also scanned the OBD and getting these codes:

Is it time for a new throttle body?

Thanks!!

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IDEngineer

· #2 · 13 d ago

Maybe just a Pedal Position Sensor (PPS) which will be far less expensive than a TB! And easy to swap yourself.

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Catsailr27

· #3 · 13 d ago

Let's start with some background. This this happen all of a sudden or gradually get worse? What shape is your battery in? If in doubt load testing is free at auto parts chains. Check ground from battery>bulkhead>engine.

When you replaced your plugs how did the old ones look? Did you slather the coils with noox when reinstalling?

Remove TB connector clean with electrical contact cleaner and then treat pins with Deoxit or Stabilet22. I would also check the TB for loose bolts on the inside per turbophil. Check Engine Light: Throttle Position Sensor issues.

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MikeNa

Discussion Starter · #4 · 13 d ago

Catsailr27 said:
Let's start with some background. This this happen all of a sudden or gradually get worse? What shape is your battery in? If in doubt load testing is free at auto parts chains. Check ground from battery>bulkhead>engine.

When you replaced your plugs how did the old ones look? Did you slather the coils with noox when reinstalling?

Remove TB connector clean with electrical contact cleaner and then treat pins with Deoxit or Stabilet22. I would also check the TB for loose bolts on the inside per turbophil. Check Engine Light: Throttle Position Sensor issues.

Great tips! Thanks!
I've done all of the above sans opening the black cover and checking the screws. Will do that today.
I'll report back. Thanks again

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IDEngineer

· #5 · 13 d ago

If that doesn't fix it, check the contacts on the PPS (senses your pedal position). I'm presuming this is a 2006+ model year. The codes you reported mention both TPS and PPS so if one doesn't fix it, the other should be checked too.

Odd that they don't have unique codes for PPS and TPS. They are entirely separate and the ECU can easily differentiate.

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MikeNa

Discussion Starter · #6 · 13 d ago

Just got done opening the throttle body, all screws are tight and no visible corrosion inside.

I then tried to blip the throttle with the engine off. If I press slowly and hold it at WOT the throttle plate would open progressively and smooth. No problem.
However when I stab it quickly and hold it down at WOT the throttle plate would oscillate (see video) Throttle Plate Oscillating

I think we can safely omit fueling or spark problem at this moment. Pretty sure it's either the TB, pedal position sensor or the wiring in between.

My lithium battery is fully charged. Always on CTEK anyway.

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IDEngineer

· #7 · 13 d ago

Need a scope on the signals to know for sure which sensor is causing that. The PPS reports what your want to the ECU, and the TPS reports what the valve is really doing. The ECU basically tries to "match" the second to the first, with some algorithms in between based on engine conditions.

If I had to guess, I'd fault the TPS. An easy scenario would be that when you punch the pedal the ECU tries to get the valve to react faster too, but if the TPS reports invalid data the ECU may cycle the valve as an attempt at recovery. It's harder to explain this behavior based on PPS failure, because if the PPS fails the ECU shouldn't command the TB to do anything... after all, what would be the "correct" throttle setting when the PPS data is corrupt?

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MikeNa

Discussion Starter · #8 · 13 d ago

IDEngineer said:
Need a scope on the signals to know for sure which sensor is causing that. The PPS reports what your want to the ECU, and the TPS reports what the valve is really doing. The ECU basically tries to "match" the second to the first, with some algorithms in between based on engine conditions.

If I had to guess, I'd fault the TPS. An easy scenario would be that when you punch the pedal the ECU tries to get the valve to react faster too, but if the TPS reports invalid data the ECU may cycle the valve as an attempt at recovery. It's harder to explain this behavior based on PPS failure, because if the PPS fails the ECU shouldn't command the TB to do anything... after all, what would be the "correct" throttle setting when the PPS data is corrupt?

Sprayed DeoxIT on the PPS sensor (pedal) connectors. Didn't fix the problem.
Listening carefully I've also realized that when the throttle plate is oscillating, the fuel pump would reset. This must have been the cause for loss of power that I'm experiencing when driving. Probably a safety feature from the ECU.

I follow your logic on the TPS vs PPS, so I should replace the TB right? It is more expensive but I guess it's much easier to do vs the pedal assembly swap??

Is replacing the PPS (throttle pedal assembly) a front-clam-off procedure? I can easily see two nuts holding it on the front and there must be another two at the rear. But the bolts heads seems to be on top of the front chassis. Maybe accessible from the wheel well?

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IDEngineer

· #9 · 13 d ago (Edited)

The PPS is part of item 15 in that image. I'm not near an Elige right now but expect #15 to be under the dash. If you want to replace it, I'd seek to replace just the dual pot and not the whole assembly. Very likely it is an off the shelf part.

I still think the TPS is more likely, though. No reason to suspect the TB (yet), the actuator appears to be working just fine.

You've only messed with the connectors. The elements and wipers are much more likely to be the culprit. But the sensors are not serviceable, so you would need to replace each sensor as a unit. Not necessarily the whole pedal assembly nor whole TB, just the sensor(s).

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MikeNa

Discussion Starter · #10 · 12 d ago

IDEngineer said:
The PPS is part of item 15 in that image. I'm not near an Elige right now but expect #15 to be under the dash. If you want to replace it, I'd seek to replace just the dual pot and not the whole assembly. Very likely it is an off the shelf part.

I still think the TPS is more likely, though. No reason to suspect the TB (yet), the actuator appears to be working just fine.

You've only messed with the connectors. The elements and wipers are much more likely to be the culprit. But the sensors are not serviceable, so you would need to replace each sensor as a unit. Not necessarily the whole pedal assembly nor whole TB, just the sensor(s).

I believe both the PPS and TPS only comes as complete assemblies (TB and Pedal box).

Tried cleaning the ECU connectors and managed to break one of the locking levers 🤦‍♂️.
I found what seems to be silicone sealant in the ECU pins. What are these and where is it coming from?? Still the same problem after cleaning the ECU connectors....

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IDEngineer

· #11 · 12 d ago

That may be how Lotus sells them, but the sensors themselves are standalone parts they bought from someone. There may be a part number or other ID on the sensors. Worth quite a bit of money to check!

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Catsailr27

· #12 · 12 d ago

My F250 had intermittent lurching and periods of dead pedal that despite testing fine and having no codes proved to be the throttle pedal assembly. Two shops didn't want to change it out unless they could prove it was the problem and I was so convinced after numerous G searches finding others with same issue that I bought one off ebay for a fraction of the new price and it fixed my problem. Narrow it down and place a WTB for what you're looking for.

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