Throttle Jerkiness. Help!

[Andrew Harper]

My car is suffering from a jerkiness when driving which I hope someone might be able me with.

Firstly it\'s not the 2,000 - 3,000 hesitation that I sometimes read about .This is slightly different.

When I come on or off the throttle I can feel a slight "stumble" from the car almost like the throttles are closing too fast.

Puzzled as to what it may be. The car runs perfectly well otherwise smooth idle, no smoke or water loss. It\'s had it\'s service recently so new oil, filter, fuel filter and plugs (problem was there before).

Changed the dash pot (as recommeded in the service manual) made no difference.

I have read about the TPS but have checked this and found no problems.

If anyone can offer any help I would be grateful.

Car details;
1996 UK Car
24,000 miles
Intake kit (Gruppe M Carbon Intake)
HKS SSQV Valve
I have removed the UIM and polished it (maybe something wrong gone here?)

Apart from that the car is as standard.

I seem to remember the problem started as I was driving to Portsmouth and I noticed the car was difficult to drive on part throttle in traffic.

Could a solenoid valve be faulty?

[Andrew Harper]

Anyone got any ideas?

Have posted this subject on the US forum as well, where it seems to be a common thing with most 3rd gens.

[RobbieRX-7]

tps (throttle position sensor) prob needs adjusting

http://www.rx7club.com/showthread.php?t=170731

[shaunwil]

I had this when i forst got mine, its more like it feeling it wants to go off the throttle and its like the clutch is very jumpy. Mine seem to disapear once i\'d used a bit. I think sometimes its just saying it needs to be used and is just a character of the car.

I get it now and again like it feels very lumpy and i now have an uprated clutch. It disapears as quickly as it comes.

shaun

[shaunwil]

Sorry, just reread your thread. There is a damper on the front of the throttle body that decellerates the butterflies when you let off, maybe you need to raise that up a little to slow down the butterflies.

Shaun

[Andrew Harper]

Thanks guys,

You could be right, I don\'t get to drive the car a lot so I suppose it could be a bit grumpy with me!

Yep the damper is the dash pot, replaced it and have adjusted it to the specs in the service manual, maybe I\'ll try adjusting it some more to see if it works.

Tested the Throttle Position Sensor with a voltmeter and everythings ok.

Thanks

Andrew.

[Andrew Harper]

Ok, a bit to add to this one.

Adjusted the dash pot and checked the TPS again, thought it had made a difference but the problem still seems to be there.

I\'ve noticed that if I\'m in say third gear at 3-4,000 rpm and come off throttle the car does not slow down smoothly it kind of stumbles as the revs decrease. As the car slows down the effect gets worse.

If I press the clutch in the effect dissapears.

I\'m starting to wonder wether the intake kit is making the car run lean at low rpm\'s.

I do still have the original airbox, would just be a pain putting it back!

[strange_days_uk]

I have the exact same problem.  Really annoying in slow traffic when you are on and off the throttle, the car can jump around a bit, and I fear it will damage the drivetrain.  I have always thought it was one of two things:

Either a slight mis fueling at very low revs, clogged injectors perhaps.
Or, a problem with the drivetrain, maybe the diff is about to go!

Have had it on other old cars, where they have done a few miles, I often think the previous driver hasn\'t been smooth on and off the throttle and that is just how the car drives now.  Let me know if you fix it.. ??

[Andrew Harper]

Read a couple of threads on RX7Club about a similar problem. It could be caused by the engine and transmission moving slightly under acceleration/decceleration.

I believe the FEED engine brace (and other makes) appear to help with this problem.

Also upgraded polyurethane engine mounts could help with this as well.

Not something I looking at doing right now, but if anyone has used these items on their car I would like some feed back.

Thanks again.

[strange_days_uk]

Sorry, just reread your thread. There is a damper on the front of the throttle body that decellerates the butterflies when you let off, maybe you need to raise that up a little to slow down the butterflies.

Shaun

Andrew any update on this ??

I have looked at this damper and it does look a likely suspect.

But I also have the problem coming on the throttle.  If I let off in traffic, 2nd or 3rd, then come back on the throttle as gently as poss, I will get a lurching/jumping for a second or two before smooth acceleration.  It is really annoying, and I\'m sure it\'s damaging the drive train.

Can anyone help please ??  :2Mad

[Andrew Harper]

Hiya,

Sorry to say I haven\'t had any luck so far with this.

You\'re right it\'s a problem that makes you worry about snapping the transmission in half! It can sometimes be that bad.

The service guide has some interesting suggestions, but most of them seem to require the use of the diagnostic equipment that the service team use.

I was hoping someone from one of the RX7 Specialists might offer a solution to this common problem.

The best way I can describe it is as follows (see if you agree);

1. On acceleration there is a slight delay with the throttle of about 1-2 seconds and then the power comes in quickly. Also anything below 2,000 rpm results in very little torque, so the car wants to stall.

2. On deceleration the car starts to shudder below the 2,000 mark in 1st, 2nd, or 3rd gear. It\'s still there in 4th but just not as noticeable.

The delay makes me think it\'s something to do with the double throttle control maybe?

Damn why does the throttle on our car have to be so devilishly complicated. haha!

I could keep changing sensors like there\'s no tomorow, but that could be very expensive.

I understand the O2 sensor can wear out, been thinking about changing that (about £40).

Slightly off topic but relevent to this, when you check the engine codes can someone tell me where the engine check light is cause I haven\'t seen it yet! I need to know I\'m looking at the right place on the dashboard.

If I\'m feeling really brave I might let the Mazda garage look at, at least they have the technical equipment needed.

Thanxs.

[Bobfish]

I have the same problem, with freshly cleaned injectors, a freshly rebuilt engine, a brand new 02 sensor and brand new turbo and idle control solenoids.

Im pretty sure the problem is just slop in the drivetrain. My next line of offence is going to be changing my engine mounts - i used to have a similar problem on my old vauxhall nova (2.0 litre 16v turbo engine) and changing the engine mounts for uprated items cured the problem. Not sure if changing them out for standard items would have helped but i know it cured it changing them.

P.s my engine mounts are knackered on the rex. Have you checked yours?

[strange_days_uk]

No I haven\'t, what about an engine brace would that work as well as new engine mounts do you think ?

[Bobfish]

May well do. Im pretty convinced as i say that its slop in the drivetrain. I.e driving along, engine is loaded torsionally in one direction, you brake, which loads it in the other direction and the idle tries to compensate, which makes the engine jump the other way, which the idle then lifts right off because of, repeat process.

I.e the engine is twisting like its doing the twist again like it did last summer, which makes the car jerk like a mofo.

[strange_days_uk]

Someone should turn down the volume then..