Strange Issue with hesitation on only light throttle

[Z-Kev]

I have checked for codes and there are none, Its a funny one where at the very barest touch of the pedal it starts to go lumpy and wants to stall, if I go past this position it runs fine no issues whatsoever, does it in all gears at all speeds but only at the lightest touch of the throttle, I am leaning towards the tps but any input is good, just had new plugs as well.

[crazydriver81]

Same issue here with my car, plus it ocassionally stalls when coming to traffic lights. Gets worse as hotter outside temp gets. Waiting for a MAF sensor to ckeck as I believe this part is faulty.

First will be to check TPS settings and check for any leaks. (I have don with no change at all)

Not much of help I know, but I am also interested if someone has experienced and cured that issue.

[Z-Kev]

Thanks , let me know if maf cures it for you mate, think i might con check the maf wiring just in case

[swinks]

I have checked for codes and there are none, Its a funny one where at the very barest touch of the pedal it starts to go lumpy and wants to stall, if I go past this position it runs fine no issues whatsoever, does it in all gears at all speeds but only at the lightest touch of the throttle, I am leaning towards the tps but any input is good, just had new plugs as well.

Have you checked fuel pressure?
Had similar symptoms when my fuel pressure was adjusted to low.

[swinks]

Same issue here with my car, plus it ocassionally stalls when coming to traffic lights. Gets worse as hotter outside temp gets. Waiting for a MAF sensor to ckeck as I believe this part is faulty.

First will be to check TPS settings and check for any leaks. (I have don with no change at all)

Not much of help I know, but I am also interested if someone has experienced and cured that issue.

Stalling under braking, i.e. traffic lights I've cured by adjusting again idle base revs on throttle body. After replacing engine mine were too low, 650 on manual so adjusted them to 800.

[Z-Kev]

thx swinks, will get a gauge onto it, possibly standard pump is going or the standard regulator could be failing might just do a filter change anyway

[Nick Mann]

I've got this now. And lent my lead out so can't check what is going on with Evoscan. The car idles fine, comes to a stop without stalling, but goes VERY rich with small throttle applications. If the car revs over approx 3000rpm then all is fine but sometimes getting the engine past 1500-2000rpm is impossible due to the over fueling. I can hear a clicking in the engine bay, so I was thinking that the stepper motor is doing something weird, but I can't quite tell where the clicking is coming from. It sounds like the stepper motor area.

[Nick Mann]

Kev, what did your issue turn out to be? My air filter is fine, my fuel filter is not that old. My wideband tells me that I am overfuelling on light throttle applications. My boost/vacuum gauge is showing solid vacuum at idle and plenty of boost on full throttle.
Disconnecting the MAF stops the issue from happening and also stops the clicking in the engine bay, although the car runs badly with the MAF disconnected.

So at the moment I think the engine bay clicking is linked to my problem. If it is a symptom or a cause I don't know. It looks like I need someone with a VR4 to nip round and let me borrow parts, as I haven't got a spare MAF to try. Or maybe even someone with all the hardware to run evoscan. (JASON!!! @foxdie )

[swinks]

Nick, that sounds like either tps off scale which makes stepper motor gone mad, or stepper motor itself. If those two are OK, them I'll look at maf issue.
BTW, any air leak between MAF and turbos (usually that rubber 3-way big pipe) may give you similar issues, good vacuum and steady boost if air leak is moderate. Got this in the past where maf wasn't sitting properly in that rubber snorkel.

[Nick Mann]

Yeah, I was thinking about the same three things. I was hoping if I could borrow a cable for evoscan I could see what the tps and maf were doing, so try to work out why the stepper motor is going mad. (I think it is the stepper motor that is clicking like a lunatic when the car is overfuelling to the point of stalling.) I may have to get the multimeter out and see if I can do it old school.

I drove into Birmingham today, arrived at 10:00 and parked up, got back in the car at 14:00 and since then the car has been playing up. So whatever went wrong happened between 9:59 and 14:01 today.

I guess it will be the weekend before I can get a few hours to investigate further, so I will be researching multimeter values before then! I'll fire up the compressor too and do a boost leak test. Plus check the pre-tub pipework as you suggested. Thanks for the input!

[foxdie]

I always noticed that, in particular with an engine that has got quite warm, stopping and then starting later would result in skewed fuelling, often running significantly lean (18+:1) for a small amount of time or until the throttle was given a good blip first.

I haven't heard of the TPS causing a tapping noise, I'd say its probably more likely that aftermarket boost solenoid we fitted for you Nick (if you remember, mine was horrifically noisy when bolted to the front strut brace, but then I remember you tried to mount yours someplace quieter.

You're welcome to borrow my OpenPort cable if you need to, do you have a laptop to run it with though? Mines currently deskbound being used for some development work. One of the first things I would check is the duty cycle of the solenoid when you hear the tapping.

May be worth removing the stepper motor, stripping it down and cleaning it out, re-greasing it with a water-resistant very slippery grease.

Ps. Have you had the battery off recently?

[Erni902]

It looks like I need someone with a VR4 to nip round and let me borrow parts, as I haven't got a spare MAF to try.

Nick, I will be fairly close this weekend but only have 1 of the VR-4's with me and at present it is not taxed or insured due to the front wheel bearings not being changed for a few weeks (only way I could stop myself driving and breaking it was to declare sorn and not renew insurance lol)

If you can come up with a list of bits youd like to try then I can remove them from the VR-4 and bring them down to you at the weekend sometime. I am about all day Sat and Sun.

[Nick Mann]

Jason, I have got a laptop, just no cable.

This is not a normal runs a bit lean on warm start up. This is runs absolutely fine on anything except low revs light throttle. When low revs and light throttle is reached it goes VERY rich, the wideband flatlines at 10.0 If moving in gear the car pops and stutters with no power, if in neutral the engine stalls. I think if the car was auto it would stall even in drive.

I wonder if it is the boost solenoid? Although I'm not sure how much it should be clicking with little or no load. It's an interesting idea that should be easy to work out - I can disconnect it and try again. I'm sure it's not the TPS clicking - there must be some kind of solenoid causing the click and the TPS doesn't have one. But it if it the stepper motor clicking, why is it? Bad stepper motor, bad TPS or bad MAF? Evoscan might be able to tell me.

Rikki, you are a gent and a scholar! Let me investigate a bit and I'll see if I need anything. I might try and investigate the stepper and TPS before the weekend.

[Erni902]

No worries mate just give me a bell if you need anything.

Since you mentioned that it would possibly stall in Drive if it was an auto it jogged my memory. I had pretty much the same symptoms, although I never had my wideband fitted so do not know about AFR's when it happened.

It did however act fine on idle and fine on WOT but low revs and light throttle it would die. When coming to a stop in Drive it would stall. Every set of lights/junction etc she would die regardless of gear etc. I removed the stepper motor and gave it a good clean (soaked it for a bit in Coca Cola (other brands are available) and the carbon came right off). I also replaced the 'O' Ring with a new one and refitted the stepper motor. This happened just after the 10th Anny Meet and has been fine since.

If you don't get around to investigating the Stepper before the weekend let me know and I will bring a new 'O' ring along with me as I think I have a spare one here.

[Erni902]

Forgot to mention that I did not notice any clicking when I had the other symptoms but it would make sense that it could be the stepper as the solenoid, nipple bit moves in and out.

Apologies for the completely non technical descriptions I left my brain at work when I finished. (arguably my colleagues may say I didnt leave it there either lol)

[Nick Mann]

Heh! Technical descriptions are often over rated! I can't hear the clicking in the car, only when I am leaning over the engine bay revving the engine from the throttle cable.

[swinks]

Nick it's more likely stepper motor, shouldn't click once engine runing, only after switch off, or before engine start after key is in position ACC/IGN.

[Nick Mann]

Yeah, I'm just not sure if the clicking is the stepper motor yet. I'll have another look as soon as I get the chance.

[foxdie]

I can't hear the clicking in the car, only when I am leaning over the engine bay revving the engine from the throttle cable.

I'm actually convinced this is now the boost solenoid. Raul used to do the exact same thing. When you twist the throttle it'll either click or lock shut, then releasing the throttle it would click repeatedly until the car reached idle then stop. Presumably because on overrun the car is below boost target and tries to build it.

Regardless, this is a symptom and not a cause. A good EvoScan log will be the best way to get some tangible info.

What you doing tomorrow or Thursday lunchtime Nick? If you could limp the car to the JQ of Birmingham I can give you time on my lunch breaks and decouple my dev laptop if needed.

[Nick Mann]

Thanks for the offer, Jase, but I'm not happy to drive the car. If I stop it is very difficult to get moving again. I have to coax the revs to get them above 3000 without stalling the car. Then I have to floor the throttle and let the clutch out. I did a couple of those in a row in traffic this afternoon, so had no choice but to slip the clutch. The clutch was not smelling good!

I'll endeavor to investigate the source of the clicking tomorrow, hopefully with a clean (or a change if I can find one in the garage) of the stepper motor and a multimeter on the TPS thrown in. I'm sure I can figure it out, but I am also sure that plugging in evoscan or swapping the maf would help me diagnose it quicker!