I have an 88 Coupe and am having problems with it. This car as been running perfectly until the last 2 months. Lately it has taken to randomly starting to buck and jerk while staying as speed for a while, or while accelerating. Letting off of the gas and depressing the pedal will fix this issue for a few minutes at which point it will happen again. Now this is not a constant problem as sometimes I will drive the car and it will perform without the slightest problems. I would like to hear peoples ideas on this issue.

I've had four things cause this over the years.
1> TPS 2> EGR 3> Ignition Coil 4> Ignition Module

1: the Throttle Position Sensor. the light throttle area gets the most wear. being thats where EVERY pedal throw starts & ends. when the beginning area gets worn down - the ECM does not know to make the proper fuel mix & timing advance for the opening throttle.
2: Exhaust Gas Recirculation is most active when engine is warmed up & running at light throttle. it makes a timing advance & a fuel leaning. if the exhaust gasses are not making it into the intake, but the timing & fuel change adjustmenst are being made - it can cause pre-detonation
3: I dunno why - but did a ohm check on my coil, one of the specs seemed questionable - not actually bad - but upon replacement - my bucking went away...
4: the igntion module is a common failure, and is heat related. another symptom is a shaky tach. when it's about to leave you stranded - you will start getting backfires as well. and these backfire WILL blow your muffler open also - so dont push it. easy easy fix: its inside the dist cap.

quote Originally posted by 88Slayer: I have an 88 Coupe and am having problems with it. This car as been running perfectly until the last 2 months. Lately it has taken to randomly starting to buck and jerk while staying as speed for a while, or while accelerating. Letting off of the gas and depressing the pedal will fix this issue for a few minutes at which point it will happen again. Now this is not a constant problem as sometimes I will drive the car and it will perform without the slightest problems. I would like to hear peoples ideas on this issue.

loose plug, or bad plug wire?

It is fuel related.
Drop the tank, remove and clean the fuel pump screen(or new one)
Also check the fuel filter( maybe 1st)

I have replaced both the pump and screen with new ones about a month back. I am going to toss in a n ew inline filter tomorrow when i get the chance. if that does not help then I shall start testing out Pyrthian's ideas. On a side note, once this all started happening, my mpg went down from 24 to 25 down to 17 to 18.

2 times for me. On my '87 Duke (non-Fiero tho) my bucking was caused by 1> Fuel Filter and 2> Throttle Position Sensor.

I would like to know if the ECM has thrown any trouble codes at you?
Here is the forum link to ECM codes.
https://www.fiero.nl/cgi-bin/main.cgi?ECMCodes
What engine and trans do you have?

quote Originally posted by 88Slayer: Lately it has taken to randomly starting to buck and jerk while staying as speed for a while, or while accelerating. Letting off of the gas and depressing the pedal will fix this issue for a few minutes at which point it will happen again. Now this is not a constant problem as sometimes I will drive the car and it will perform without the slightest problems.

I was going to suggest the fuel pump, but you've already replaced it. Since your fuel economy has worsened, it's possible that one (or more) of your engine sensors may be out of whack, making it run rich. If you have access to an OBD-1 scanner, you should be able to find the culprit.

Best of luck!

[This message has been edited by Blacktree (edited 03-19-2008).]

Other things to look for are.

This sounds stupid but.

Like above first check for codes then disconnect the battery. By disconnecting the battery you reset the computer back to factory specks. The computer has the ability to learn bad things.

Now when you check for codes you might find 14 or 15 but even if you don't the coolant sensor can go bad and tell the engine the temperature is low and give you way to much fuel (in burst).

If you have an automatic trans the transaxle converter clutch can also cause this. You can just touch the brake to release the TCC. If it makes the problem go away it could be the switch, solenoid or 3rd gear switch (in the trans).

Ed

EDIT: Blacktree I was typing while you posted ...slow typer.

[This message has been edited by Fino (edited 03-19-2008).]

I have had the same problem a few times and it was always the plug wires. They are easy to check and not that expensive.

quote Originally posted by anthony_86gt: I have had the same problem a few times and it was always the plug wires. They are easy to check and not that expensive.

Same thing with me. I've had bad plug wires once, and loose plug twice. Definitely something worth checking.

quote Originally posted by Pyrthian: I've had four things cause this over the years. 1> TPS 2> EGR 3> Ignition Coil 4> Ignition Module 1: the Throttle Position Sensor. the light throttle area gets the most wear. being thats where EVERY pedal throw starts & ends. when the beginning area gets worn down - the ECM does not know to make the proper fuel mix & timing advance for the opening throttle. 2: Exhaust Gas Recirculation is most active when engine is warmed up & running at light throttle. it makes a timing advance & a fuel leaning. if the exhaust gasses are not making it into the intake, but the timing & fuel change adjustmenst are being made - it can cause pre-detonation 3: I dunno why - but did a ohm check on my coil, one of the specs seemed questionable - not actually bad - but upon replacement - my bucking went away... 4: the igntion module is a common failure, and is heat related. another symptom is a shaky tach. when it's about to leave you stranded - you will start getting backfires as well. and these backfire WILL blow your muffler open also - so dont push it. easy easy fix: its inside the dist cap.

I too am having bucking, but always at very low throttle. Ignition is not to blame as plugs, wires, and coil were replaced very recently. TPS I can try to diagnose with another TPS by connected it to the old one and moving it with my thumb as I push open the throttle. EGR, without removing it, how do I test it? By running premium and seeing if it stops? (I recall if you cap off the EGR completely you have to run premium or it knocks)

quote Originally posted by AP2k: I too am having bucking, but always at very low throttle. Ignition is not to blame as plugs, wires, and coil were replaced very recently. TPS I can try to diagnose with another TPS by connected it to the old one and moving it with my thumb as I push open the throttle. EGR, without removing it, how do I test it? By running premium and seeing if it stops? (I recall if you cap off the EGR completely you have to run premium or it knocks)

there are 2 parts - the solenoid & "the mushroom"
if the solenoid fails - it'll set a "check engine" code.
the solenoid moves the mushroom thru a vacuum line. make sure the line is intact.
next, make sure the actual diaphram in the mushroom can move. it can easily be completely full of soot. same for the actual tube which goes from the mushroom to the upper plenum. they are often fully clogged with soot.

quote Originally posted by Blacktree: Since your fuel economy has worsened, it's possible that one (or more) of your engine sensors may be out of whack, making it run rich. If you have access to an OBD-1 scanner, you should be able to find the culprit. Best of luck!

I had the same problem as mentioned, and used WINADL, and found the temp sensor for the ECM was reading much lower then the actual temp was. Dash gauge and laser temp device was showing temp around 180-190, and WINADL was showing 115 or so. New sensor fixed my problem.

Kevin

quote Originally posted by 88Slayer: I have an 88 Coupe and am having problems with it. This car as been running perfectly until the last 2 months. Lately it has taken to randomly starting to buck and jerk while staying as speed for a while, or while accelerating. Letting off of the gas and depressing the pedal will fix this issue for a few minutes at which point it will happen again. Now this is not a constant problem as sometimes I will drive the car and it will perform without the slightest problems. I would like to hear peoples ideas on this issue.

Which engine and trans do you have?

Ed
EDIT: I found it: It is a 2.4
https://www.fiero.nl/forum/Forum2/HTML/090212.html

[This message has been edited by Fino (edited 03-19-2008).]

If your cars doing what I think it's doing mine did the same thing. Mine turned out to be the egr(its a 4-cylinder btw). I have no idea what was actually wrong with it, but when i compared it to another one it was a lot easier to push open and wouldn't hold pressure, though it would still open under vacuum when the engine was running.

For those who are asking, I have the 2.4l Tech 4 'Iron Duke' engine mated to the Isuzu 5spd man. trans.

quote Originally posted by anthony_86gt: I have had the same problem a few times and it was always the plug wires. They are easy to check and not that expensive.

quote Originally posted by 85fiero_fanat: Same thing with me. I've had bad plug wires once, and loose plug twice. Definitely something worth checking.

quote Originally posted by 88Slayer: For those who are asking, I have the 2.4l Tech 4 'Iron Duke' engine mated to the Isuzu 5spd man. trans.

Make it three, plug wires fixed it. I had the same engine/tranny combo.

-fh

Well, Considering all that has been sugested so far, I will replace the spark plugs and wires as well as my inline fuel filter tomorrow. If that does not work then I will start going through the various sensors to see if any are bad.

quote Originally posted by 88Slayer: Well, Considering all that has been sugested so far, I will replace the spark plugs and wires as well as my inline fuel filter tomorrow. If that does not work then I will start going through the various sensors to see if any are bad.

This needs to be repaired first.

In your other post
https://www.fiero.nl/forum/Forum2/HTML/090212.html

88Slayer : I am having problems getting my tach to read properly. When the car starts, the tach will jump from 0 rpm to pegged at max. I have been unable to find out where the sensor is for the tach and have therfor been unable to replace it. Would any of yall be able to help me locate it on a 88 2.4 Coupe?

Ed

quote Originally posted by 88Slayer: Well, Considering all that has been sugested so far, I will replace the spark plugs and wires as well as my inline fuel filter tomorrow. If that does not work then I will start going through the various sensors to see if any are bad.

You may not need to replace a plug, if you feel all of the wires and one is shaking, then that plug is loose and you just need to tighten it up. I replaced my plugs a year and a half ago, and about half a year ago I had one plug loose, and then today my car started bucking around again and a different plug was loose. Weird thing is that I replied to this post before I left in the morning and stated that a loose plug could cause it, then on my way to class I had a problem with it lol.

I got the same problem atm, sure wish guys would post up if they solved the problem and what they did!
sparx22

Mine turned out to be an issue with the whole iginition module. Had it replaced and the issues dissapeared

I experienced this one time and i think i might know the answers to some of your guys problems. I had an 87 coup and i was getting the engine prepped to be removed so i was removing all possilble things that i could think of before i drove the car to the place where i could remove the engine. I could not do it in my car port on an air force installation. The only thing i unconnected was the evap canister. Went down the road for like 10 miles then started to buck and jerk like you guys are saying. I jumped out and plugged back in my evap canister and whala it was running fine. A lot of people forget about the charcol filter in the bottom of it. I would just replace the whole canister as it is only 30.00. I think a lot of people over look this little thing. food for though.oh the engine was a 4cyl 5speed.

quote Originally posted by 88Slayer: I have replaced both the pump and screen with new ones about a month back. I am going to toss in a n ew inline filter tomorrow when i get the chance. if that does not help then I shall start testing out Pyrthian's ideas. On a side note, once this all started happening, my mpg went down from 24 to 25 down to 17 to 18.

You will void the warantee on the new fuel pump if you don't replace the fuel filter.