Hesitation/mild surging when applying throttle at cruise speed

[rowan194]

A few days ago on the freeway I was cruising at about 80km/hr, put my foot down a fair bit to get into a better position to change lanes, but nothing happened... no change in engine RPM, no trans kickdown. As I released the accel back to the position I had it in, the trans made a clunk as if it had started changing, but aborted when it realised I'd gone back to cruise speed.

Possibly related, the next day I was again already at road speed, behind a slower car, which then cleared, so I put the foot down... this time it did accelerate, but it was a bit sluggish, and I could feel the car wavering, like there was a fat guy rocking back and forth in the seat.

Have not experienced any issues like a misfire or anything noticeable when accelerating normally from standstill, it's just when cruising and I give it extra juice.

Didn't see any leadup to this behaviour, first time was sudden as mentioned above. No probs yesterday. Any ideas?

[Mr Hardware]

usual questions
how long since you replaced plugs, air filter, fuel filter, did and ISC clean, did a battery reset?

[robbyj]

sounds like a spark issue, IE what Mr Hardware said. My bet would be plugs and leads.

[dieseltrain79]

Gearbox slipping if it's not a misfire maybe .

[SirHenry]

How old is the coil pack?

[rowan194]

Coil pack, leads and sparks were replaced about a year/20,000km ago. Air filter would have been done around the same time.

Not sure about the fuel filter, would be at least a couple of years since it has been serviced at a dealer, and I haven't changed it myself since.

I'm going to attack the intake with some carby cleaner today then do an ECU reset and see what happens, but to make things more difficult, the issue hasn't happened again, apart from those 2 (separate) times. Hope it's not the trans, I'm up to 207,000km, so it would be almost geriatric by now...

[Evgeni]

Worth having a look at the TPS output and seeing if there are any flatspots. Pretty quick check - just need a multimeter and a pin.

[rowan194]

Originally Posted by Evgeni

Worth having a look at the TPS output and seeing if there are any flatspots. Pretty quick check - just need a multimeter and a pin.

Cheers. Didn't think of that. If the output is a little dodgy it would explain why the trans didn't even thinking about kicking down until the point that I released the accel, maybe it didn't even see me pressing harder for those few seconds... but wouldn't the butterfly being physically further open still do something to the engine revs?

[SirHenry]

Originally Posted by rowan194

Coil pack, leads and sparks were replaced about a year/20,000km ago. Air filter would have been done around the same time.

Not sure about the fuel filter, would be at least a couple of years since it has been serviced at a dealer, and I haven't changed it myself since.

I'm going to attack the intake with some carby cleaner today then do an ECU reset and see what happens, but to make things more difficult, the issue hasn't happened again, apart from those 2 (separate) times. Hope it's not the trans, I'm up to 207,000km, so it would be almost geriatric by now...

Nah mine's up to 240k and still going strong, just keep it serviced.

Sounds like good plan of attack

[Evgeni]

Originally Posted by rowan194

Cheers. Didn't think of that. If the output is a little dodgy it would explain why the trans didn't even thinking about kicking down until the point that I released the accel, maybe it didn't even see me pressing harder for those few seconds... but wouldn't the butterfly being physically further open still do something to the engine revs?

Yes, these things can cause a bit of havoc when they play up.
I guess with the butterfly open, you would let more air into the intake. Given the map sensor is in the intake, it would register and it would raise the rpm. Suppose if the TPS was not corresponding to this action, things like the injector pulse, gear selection would not necessarily be able to react to your commands.
Let us know how it goes. Good luck.

[ThosK]

Hi guys
Had a surging and stalling problem. After new coils plugs etc and heartache I found the problem. There a small L shaped hose going from the air intake to the rocker cover, for cooling of the upper motor I think. The hotter the motor the more the hose sucks out of the air intake . This causes the various sensors to play up.
I diverted the little hose away from the air intake and blocked the hole . The rocker cover was then sucking air in from the engine bay. PROBLEM FIXED