mathetas

I have a 5spd (new clutch) 1990 GXL with about 2500 miles on a rebuild (145,000 on car)... The engine performs great during acceleration, with 0 hesitation or miss. However, if I ease off the gas and slow to a 'cruise' - like on the highway - the car kind of shakes if the throttle isn't somewhat being applied. I realize those symptoms could be a lot of things (or maybe even normal for the engine design - my first rx7), but I thought I might throw it out there to see if anyone has experienced a similar issue. The shake kind of reminds me of riding in a car with someone who is not good with the clutch - especially in first gear - a green-horn jerk, if you will. However, I don't want to give you all the impression the jerk is unbearable, because it's not. It's just annoying, and i don't want to be overlooking a mild problem now that might grow into a catastrophe later. Any bumps would be greatly appreciated...

Rear Brakes (and/or rotors)? Clutch Issue? Compression Issue? Tires? Warped Wheels? The Marriage of My Ignorance and Obsessive/Compulsive Sensitivity?

mathetas

I have a 5spd (new clutch) 1990 GXL with about 2500 miles on a rebuild (145,000 on car)... The engine performs great during acceleration, with 0 hesitation or miss. However, if I ease off the gas and slow to a 'cruise' - like on the highway - the car kind of shakes if the throttle isn't somewhat being applied. I realize those symptoms could be a lot of things (or maybe even normal for the engine design - my first rx7), but I thought I might throw it out there to see if anyone has experienced a similar issue. The shake kind of reminds me of riding in a car with someone who is not good with the clutch - especially in first gear - a green-horn jerk, if you will. However, I don't want to give you all the impression the jerk is unbearable, because it's not. It's just annoying, but i don't want to be overlooking a mild problem now that might grow into a catastrophe later. Any bumps would be greatly appreciated...

Rear Brakes (and/or rotors)? Clutch Issue? Compression Issue? Tires? Warped Wheels? The Marriage of My Ignorance and Obsessive/Compulsive Sensitivity?

Molotovman

iTrader: (49)

My car does the same at low speeds. I'm just going to guess the car doesnt like to be off the throttle and moving.

13bpower

It would be the last one you mentioned.

Your car cuts fuel to the rotors when you are cursing. It is much more evident on a car with a loud exhaust. You can hear the pitch of the exhaust change as the ECU cuts fuel to the rear rotor and then the front as well.

You have nothing to worry about. It is just part of the personality of the car.

mathetas

Have you experienced the same feeling riding in someone else's rx7? I wonder if that is a 'normal' issue?

mathetas

my computer is holding replies... then duplicating them... sorry

fg0d

Same thing happens to me, under any driving. If I lift off the throttle it has a little stopping motion. No clue what its from but it happens and I dont mind.

NZConvertible

That's not entirely correct. It can be fixed to a degree.

The injectors are switched off when you close the throttle to save fuel, and switched back on when you open it or the engine drops below ~1500rpm. The point in the throttle travel at which the injectors are switched on and off depends on the adjustment of the TPS. If it's out of spec, driveability will be affected as described. When it's set right, the transition is much less noticeable.

MechE00

If this is what I think it is, it happens more at low speed/low gears than at high speed/gears, then you are just dealing with play in the drivetrain/motor mounts.

If it is excessive, you might want to check your motor mounts to see if they need attention, but otherwise I think it's pretty much what all manual transmission cars will do..

please someone correct me if I'm off base.

mathetas

I've had several 5spd automobiles, and in low gears and high rpm's, I totally agree - I think that is normal. But, my car does it a low rpm's in every gear. Granted, it does it more in low gears and high rpm's, but it does it in high gears as well... I might look into checking the drivetrain/motor mounts... More bumps?

HAILERS

Dittos to what the NZ guy said.

mathetas

How would I go about adjusting the TPS to spec?

elfking

I had the same symptoms you were having and as soon as I set my TPS it did infact fix this problem as well as some off and on idle annoyances... If you search for TPS setting/calibrating you might find some more info, I had a quick link on hand:

https://www.rx7club.com/showthread.p...TPS+Adjustment

More directly I used these instructions from further down on the page, they are great to have handy:

Enjoy.

introVert

My 88 vert does it, too. I hear it is exacerbated by having dirty injectors. I just keep my foot in it a little at all times

mathetas

Thanks for the advice... I've got a flathead screwdriver and an ohmmeter sitting here next to my computer. Tomorrow, or perhaps Tuesday, I'll try to find the half hour to test it. I'm not too deft with working on this thing yet, but I'll give it a shot... Thanks to everyone for your input. You all sure do save a guy like me a lot of money not having to consult my local rotary 'expert'. I'll post the results after I complete the test.

elfking

The only thing I might add to it is if you have any terminal connectors. The female part of it which would plug onto most after market speakers, they will fit on the TPS connectors. If you are having problems getting a good reading from it, you can hook those not all the way just enough to hold on the connector. Then use your ohmmeter on the connectors.. Since I only had myself holding 2 connectors and turning a screw was a bit easier that way...

mathetas

Whattayaknow... Got three extra packs of those connectors last week for a set of speakers from Crutchfield... I'll be sure to put them to use. Thanks again, to everyone - especially you elfking.

GTUser

Hey, Mathetas, thanks for asking the question. My 89 GTU has done this since I got it and I have assumed that it is just the way the car drives at low Rpms in a low gear. It just goes to show, if you don't ask, you will never find out things.

Terrh

iTrader: (7)

check your motor/transmission mounts too... they can cause a TON of drivability issues... engine rocks which causes the throttle to move a bit which makes it rock more etc etc etc and it turns into hell, lol

GTUser

I was just out looking at some stuff and running copies of interesting things in the service manual for 89-91 FCs at this link: http://www.teamfc3s.org/main/factory..._non_turbo.pdf

Look at pages F1-71 & 72, this specifically discusses the Deceleration Control System and how to adjust and troubleshoot for the engine "bucking" as it slows down.

pmr2000

Definitely TPS, everyone should adjust before trying anything else, I did my with the led light method and it cured the jerkiness in 1st and 2nd gear.

Parastie

I'd have to go with NZ, i had a similar problem and spent an hour adjusting TPS and idle until i had it just right. Now it's great!

SureShot

Ahh - RTFM - I had overlooked the dash pot's setting.

lnbrown5981

i believe the bucking and jerking on throttle release is from an incorrectly set or non existent dash pot. the dashpot stops the throttle from snapping shut when released. when my car did this i readjusted the dashpot via fsm and voila it went away. then i did the tb mod and eventually took it off all together. i like it better without it, heps to shoot flames too

Radial GT

iTrader: (16)

if the tps is set correct when you let off it will kick in engine drag mode (uses the engine as a brake). sounds like your tps is thinking differently