Confusing the issue of the poor idle has been the exhaust, which started blowing not long after the cold weather when I was using Cold Start spray because the car wouldn't start - I have wondered whether this is related, and sped up the damage to the exhaust in some way (that Cold Start stuff is really explosive!).
Anyway by the time I was ready to fix it, the back box and the incoming exhaust pipe had totally separated due to rust around the join. I bought a new back box via ebay for £80 including gasket, and last weekend was all set. I knew I could get under the car well enough to do the job by parking it with both nearside wheels on the kerb, and just needed the rain to stop. It didn't, so on Sunday I decided to do it anyway. It was fairly simple - three bolts holding the box to the chassis (via rubber hangers), and another three where the pipe joins the pipe exiting the catalytic converter.
Apart from one of the bolts on the pipe, which was so badly corroded it had to be sawn through, it went smoothly. However, it was quite slow going, and I was thoroughly soaked before I'd got halfway. But it was worth it and the car sounds 1000 times better, although with a little rattling. This seems to have been caused by a bracket on the new exhaust being positioned slightly off, so that it was in contact with the frame, and hopefully is now fixed.
I still have to replace one of the bolts on the pipe, and add spring washers, as the previous ones currently on there are finished.
The main problem this car has suffered since I bought it has been its poor idle. For the first six or so months, it ran absolutely fine, but then it began to stall regularly when idling, and it's steadily got worse. Even now it's got warmer has not improved, and happens equally whether the engine is warm or cold.
The stalling problem did not appear to be a physical issue with the overall running of the engine which remained smooth and even when under power. It appeared to be more to do with the ECU's ability to control the throttle when the pedal is released.
As soon as I take my foot off the throttle, the RPM needle drops rapidly, sometimes stopping at a healthy 800-1000, sometimes stopping really low at around 500 RPM, and at other times not stopping at all and resulting in a stall. It seems like the throttle cannot open and close freely, preventing the motor that operates it (via the ECU) from making fine adjustments accurately.
These cars do have a bit of a reputation for fuel system issues - particularly in the throttle body - which apparently arise due to differences between European fuel and its Japanese counterpart. Jap fuel is more highly refined than European (presumably because of the terrible smog Tokyo used to suffer from) and has far less unwanted extras like sodium in the mix.
compton
9:37 pm, Tuesday, 23 May 06
Removing the large air intake is simple enough once the two collars on either end have been loosened. The body itself is held onto the engine block with four bolts; however it's linked in to the cooling system, and there are smallish hoses leading in and leading out.
These hoses are full of coolant of course, and recommended procedure is to clamp them off so that they can be unplugged from the throttle body without having to drain and then top up the coolant.
If you don't have clamps and are a bit lazy like me, you can actually get away with leaving the hoses attached. Undo all four bolts, and gently pull away the throttle body unit so as not to damage the gasket. You can now use liberal blasts of the carburettor cleaner spray on the throttle itself. As you blast away, pull and release the cable to work the throttle and allow the spray to penetrate the hinge mechanism better.
Make sure to blast it from both sides - as it's now detached from the engine block you should be able to pull it away enough to give sufficient access for the spray can. You should be able to see in as well, and you can verify the removal of all the blackened soot and gunk.
Obviously don't cheap out on the spray now you've got good access to the throttle - I used about half the can before it was as clean as it was going to get. The excess solvent should be dripping harmlessly onto the ground as well, because the body is not attached to the block. When you're happy, leave it 10 minutes for the solvent to evaporate, then refit everything and give it a whirl.
If you're not lazy, or you just want to do it properly, then clamp the hoses and fully remove the throttle body. Give it a clean, and leave it submerged in petrol overnight before a final thorough cleaning.
I also put in new NGK spark plugs (IZFR-6B), which seem far more suitable to this car than the more expensive Bosch plugs, again Halfords. Total cost £20, 90 minutes on the drive. Bargain! This site appears to sell suitable spark plugs at a good price also.
The other weakness of the GDI engine is coking - deposits of carbon building up around the injectors and impeding the flow of fuel through them, caused by Europe's relatively dirty petrol. Many petrol stations sell more expensive 98 RON petrol (eg BP Ultimate, Shell V-Power), which as well as having a higher octane rating also has less of the impurities. I do tend to use this, although I can't say how much difference it makes. It certainly won't clear any clogging already done, but it may well be worth the extra expense for this particular car.