99 1.3 Corolla 4E-FE engine - possible detonation, surging

Question

Sorry for joining up and immediately asking a question but I'm stumped with my old Corolla.

I haven't had it very long, only doing about 1500 miles, but I've got a couple of niggling issues that have got me stuck.

The first is something I'm hoping isn't detonation. I've recorded a clip here that demonstrates the noise I'm getting. Corolla Noise

This only really happens in 4th and 5th gear between 2000-2500 RPM with load on the engine, sometimes a little in 3rd and 6th gear.

The second issue that may be related is that at around 1800-2000 RPM mark at constant speed with very low throttle input, the car jerks slightly, almost like a very light misfire/surging. If you give it more gas, it carries on. Ocassionally it will hesitate a tiny bit doing so.

After only a couple of hundred miles of me having the car, I had to change the head gasket as it blew between a coolant channel and atmosphere, so was pushing coolant out of the side of the engine. Sadly it wasn't doing this when I bought it, or for the first few hundred miles. I managed to catch it and get it done before it overheated, and both of the above issues were present before it was fixed. The car does have a full service history.

Since then I've done over 1000 miles no problem, car runs great besides those 2 issues. Returning 42 imperial MPG which is about what I'd expect and passed emissions shortly before I bought it. It has done 96k miles.

So far I've tried:

• New Denso K16TR11 plugs
• Tested the TPS, this seems OK and is working correctly.
• Oil and filter changed.
• Ran a few tanks of Shell V-Power to see if it helped, nothing really changed.
• Briefly checked for vacuum leaks and can't find any other than the first stages of the PCV return hose perishing, but didn't seem to leak.
• Checked for fault codes, nothing stored.

This engine was the latest revision of the 4E-FE we had in the UK, so it uses a crank sensor and wasted spark with ECU controlled ignition timing rather than the distributor setup on other models, so I can't adjust/check the timing.

My initial thought is that the MAP sensor is slightly out, but hopefully I'm being a little paranoid with the above noise being detonation.

Any help is gratefully appreciated, I'm a massive Toyota nut and like this car a lot, so I'd like it to last a while.

Answer 1

Did you clean the mass airflow sensor on the air intake? Was the head shaved when the head gasket was done? It is common to shave the head when it is repaired. If so, then the compression ratio could be higher than normal. You do not say how far it has traveled. On an older engine raising the compression could produce the symptoms you describe, particularly if the pistons are worn. I listened to your clip twice, but there was too much background noise to discern what the noise was. It sounded a little like some clicking noise momentarily, but I was not sure if that is what you are referring to? In any case, high compression can cause pre-detonation, although this often happens in combination with carbon build up in the head. Your head should have been De-carbonised while it was off? When you say you tried V-power, I'm assuming you mean 98 octane. Have you tried going even higher with an additive. Raising the octane makes the fuel burn slower, which helps resolve issues with pre-detonation in high compression motors. Assuming your pistons, gudgeon pins, big-end bearings and main bearings are all in good shape, and assuming that your oil pressure is good, then you are left with another issue. How are your timing belt and tensioner? The throttle position sensor might be ok, but if there is wear in the throttle body butterfly shaft, this can cause some intermittent hesitation at low revs, as can a dirty butterfly and dirty intake throat surrounding the butterfly.