Hey guys. Another brain scratcher.

My TH will occasionally drop revs for maybe half a second, then spring back up to normal revs. It's amost asif it considers shifting down for some reason, then decides not to and stays in the same gear. I noticed when I was moving quite slowly the other day (20 - 30km/h) that it even did it in first (shifter in L). It does it when I'm cruising at 80km/h and in fourth.

I've only noticed it in first and forth as I cruise in forth and accidentally stumbled upon it in first. Car shifts fine, downshifts ok too.

I need to get a transmission flush done fairly soon as the fluid looks like poo, is it likely to be this causing the issue?

And if I remember correctly, I think I've tried resetting the transmission (remove negative battery terminal) with no improvement.

Whats also funny is that a local stretch of road, I set cruise at 83ish, and almost deadset it happens at the same segment of road. Is it likely to be a shifting issue? Maybe a clutch? Is it new transmission time/time for a rebuild?

Anyone?

Car drops revs, so you think it is a gearbox problem? If the gearbox dropped out - ie lost drive - surely the engine would rev it's head off?
Don't follow that logic myself - problem with revs = engine surely?
You can probably initiate the same "gearbox problem" by momentarily turning the ignition off and on. (Not that I'm suggesting doing this.)

Had the same problem, a misfire at certain low throttle openings. Turned out to be a burnt exhaust valve.

Flush or rebuild your gearbox if you want to, but I would start by looking for air leaks, defective plug leads and spark plugs, distributor cap and rotor, then doing a compression test. And maybe checking for a coolant leak inside the car onto the ECU/TCU?

Is the stretch of road you refer to unusually bumpy? Does it occur elsewhere?
MadMax has the right of it, I'd be checking that ECU and making sure the heater core hasn't gone dodo on you.

It should be one of these. Spark plugs,leads,distributor

It may infact be the engine. I just suspected the transmission because I'm a spirited driver, it needs a flush, has nearly 275xxx KMs on it. I replaced the heater core seals about a year ago, and there was only a bit of coolant coming out. (also being a TH it has the plastic cover over the ECU, but there wasn't even enough to wet the plastic).

I do have a pod filter on it at the moment, I might try swapping that out for the stock setup. I'm about due for an engine oil change so I might do that tomorrow.

Might try the spark plugs, they might be causing issues. They were changed (I think) when I bought the car, maybe 30/40xxx kms ago.

Check your fuel filter too, though I doubt that's the cause.

It may infact be the engine.

Might try the spark plugs, they might be causing issues. They were changed (I think) when I bought the car, maybe 30/40xxx kms ago.

Gee thanks for the vote of confidence!

I think maybe, possibly, hopefully, the last owner changed the plugs just before he sold the car ?????
I doubt it somehow . . . lol

Anyway, looking at the plugs will tell you which cylinder is misbehaving.

Gee thanks for the vote of confidence!

I think maybe, possibly, hopefully, the last owner changed the plugs just before he sold the car ?????
I doubt it somehow . . . lol

Anyway, looking at the plugs will tell you which cylinder is misbehaving.

Haha, I bought it from a dealer. From my (very hazy) memory, I remember him saying something about he replaced the spark plugs. He also gave me 3 spark plugs. I think he put the good ones in the back and normal ones in the front, and I think at some point I was meant to put the new ones in...

Oh well, I bought 3 normal and 3 good ones today, will probably put them in some time tomorrow.

I'm having a similar issue 98 Sports, usually comes after a trip at >80kms/h. It's like the car downshifts then changes it's mind. Then things got worse, the car started stalling, happened at idle as well as low speed and once on the motorway. I beat the s**t out of the fuel pump wiring harness (top of the tank) and the car fired back up immediately. I've been battling this nagging issue for a few months now, trying all manner of things. It's certainly the fuel pump wiring in my case. I changed the fuel pump/tank cap/wiring connector by using one picked up from the wreckers. But I'm thinking it's an inherent design fault as it surfaced after a few months with the new unit.
I never use ethanol blend, always 95 - 98 RON.
She died on my over the weekend and with 300,000 on the clock I'm thinking of saying goodbye to the old girl.
I'll try working around the wiring harness on the fuel tank (without blowing anything up) and let you know how it goes for me.
But my issues started with a weird shift like you described.

I'm gonna go with TPS. Plugs or leads usually cause more of an engine miss or backfire than a momuntary loss of go.

An update on this, the problem is still present. The problem appears to only be present while applying very slight throttle, such as slowing down into a lower speed zone but having a bit of throttle applied.

Going to look into the TPS, meanwhile does anyone have any suggestions?

While you're investigating the TPS, if you haven't already done so you might check out the idle speed controller (ISC).

Sure enough, checked the TPS and it was not set right. Looking at it, there are white-out or paint marks on the bolts am on the plastic cover. The bolt was set to one side and the mark around half way. Corrected this, went for a 20km drive, smooth sailing.

Cheers for the TPS suggestion guys!



While you're investigating the TPS, if you haven't already done so you might check out the idle speed controller (ISC).

Checked and was fine (naturally)