Noticable momentary dip in power when accelerating/engine under load

[mickburkesnr]

A strange one this.

Before I changed the timing belt on my Corolla (1998, 1.3 4EFE engine) sometimes, not all the time, but sometimes when I applied the accelerator the engine would rev up, then the car would lurch forward as the engine revs dipped considerably and there'd be a squeak all at the same time, then the engine would return to normal. At the time I hadn't changed any of the belts, so I thought it might be a timing belt slip as it was well over 10 years since the belt was changed.

However, all the belts have been changed and tightened, and while driving the car yesterday the car did this about 3 times under acceleration. It doesn't matter what gear I'm in. It'll happen in 5th as it will happen in 1st.

So, the car has been recently serviced before I got it. The air filter is clean, plugs don't look new but certaintly not burnt out/old either. The belts have been changed, although I may need to tighten the power steering belt a bit. I'm not entirely sure why the car is doing it, would it be possible that it's a fuel filter issue or something more terminal?

[m4h00]

Are coils ok? Did all spark plugs look similiar? A while ago, while accelerating my engine would lose and gain back power within seconds. One ignition coil was faulty which I could see by simply comparing spark plugs. Replaced it, it's perfect since then. I have a different car, but issue may be similiar.

[craggle]

If a timing belt slips the engine will stop pretty quickly sometime accompanied by expensive sounding crunching noises as pistons hit the valves.

Sounds like a slipping clutch to me. It will slip when the load increases and grip again as the revs die down.

Craig.

[mickburkesnr]

I don't think it's the clutch, as it gets up to speed fine and pulls away without a problem. There is a big hill I go up on the way to work every day and the revs are always constant. The other day I went in to 5th, which I shouldn't have done, and the engine struggled which is what I expected to happen. Before I go for lunch in half an hour I'll try and stall the car in 4th see if that shows up anything with the clutch.

At the moment it will gain power, then it'll lose power like I've driven in to a puddle, then pick up again. That's the better way of describing this issue.

With the spark plugs they all looked identical. There's nothing out of the ordinary with them. Aside from this issue it starts and runs fine, and this has only happened maybe 4 or 5 times, so I wouldn't expect the ignition coil to behave like this only a small number of times?

[craggle]

Okay, That does sound less clutch like now. 

Sounds an odd problem, Fuel related maybe?

Craig.

[mickburkesnr]

I've just tried the clutch with the hand brake on and slipped it in to 4th, every time I go to let my foot off the clutch it wanted to stall, so I can rule out a clutch (thank God!).

It's a strange problem. I don't know about the fuel, it's had 3 full tanks of fuel from different stations since I had it while this problem has occured. I did put some Redex in the first two tanks, this current tank doesn't have any in. That wouldn't be a cause?

[m4h00]

I don't think it's the clutch, as it gets up to speed fine and pulls away without a problem. There is a big hill I go up on the way to work every day and the revs are always constant. The other day I went in to 5th, which I shouldn't have done, and the engine struggled which is what I expected to happen. Before I go for lunch in half an hour I'll try and stall the car in 4th see if that shows up anything with the clutch.

At the moment it will gain power, then it'll lose power like I've driven in to a puddle, then pick up again. That's the better way of describing this issue.

With the spark plugs they all looked identical. There's nothing out of the ordinary with them. Aside from this issue it starts and runs fine, and this has only happened maybe 4 or 5 times, so I wouldn't expect the ignition coil to behave like this only a small number of times?

Still sounds like my problem with one of the coils ;)

[mickburkesnr]

I'll have to get that checked, I read how to check it but it's a bit beyond me. I don't mind working with flammable liquids, but I draw the line at electrocution!

This issue doesn't seem to happen in the morning either. Every day this week I drive to work from about 6am and get in at 7pm. The car doesn't suffer from this issue. But then in the afternoon is when it happens. Maybe the heat makes the issue worse?