4AGE 20 Valve idle and running issues

[den7]

Hi, this is my first (maybe 2nd) post to the forum, unfortunately it is a problem. I replaced the cambelt in my 20 valve AE101 Corolla and now it has some issues...

I will try to list the symptoms as best as I can.

1. Known issues (prior to replacing the cambelt).

a. No 1 spark plug lead is faulty, but not completely failed.
b. Distributor cap probably needs replacing, but is functioning OK
c. Needs a new thermostat
d. Idle was never 100% (usually slightly high) and belched large amounts of black smoke at high RPMs

As for the cambelt. The engine was at TDC throughout the replacement process, tensioner pulley was also replaced. Timing was set at 10 degrees with the correct terminals shorted and the engine at close to normal operating temperature (1/2 way on the gauge)

The problem. As the car gets to temperature the idle starts to drop until it almost stalls and it is running rich (black smoke from the exhaust) which appears to be through the rev range.

The idle seems to hold steady as long as the car is not revved. Once it is revved and it comes back down to idle it almost stalls. Turning the car off and restarting it seems to improve the idle (until it gets revved again)

On the advice of a friend I loosened the oil cap and the idle came back up to normal and the car started to run better (at idle). Put the cap back on an the idle dropped again. He suggested that the car was able to suck in extra air from the cap being loosened which allowed the car to run better. Honestly, I'm not 100% sure how this works, but it seems to be a clue to the issue that its having. My first thought here is a dodgy AFM (does anyone have a link to its values for testing it?)

I have some thoughts, but just wondered if anyone could point me in the right direction here so I don't start going around in circles. Thanks

[thegreatestben]

I'm having alot of the same issues as you've mentioned in my blacktop 20v.
Idle issues are pretty much gonna be ISCV related, mine has a high idle 90% of the time and I'm fairly sure it's running quite rich.

Try removing the ISCV and giving it a clean, should come right. It didn't fix mine 100% but it certainly made a big difference.

[den7]

Thanks for the quick reply. I followed a site on cleaning the ISCV in place, so that's all done. Didn't seem to resolve the issue though. But will add it to my list for things to test

[deaf_rattle]

id check the timing again

[den7]

Hi, thanks. Timing checked again. Still at 10~11 degrees. Update, now has a fault code "12"

[AceSniper]

I'm having alot of the same issues as you've mentioned in my blacktop 20v.
Idle issues are pretty much gonna be ISCV related, mine has a high idle 90% of the time and I'm fairly sure it's running quite rich.

Try removing the ISCV and giving it a clean, should come right. It didn't fix mine 100% but it certainly made a big difference.

Your problem might be the ecu temp sensor.

code 12 seams to be ign system, does the engine miss when you give it some revs?
removing the oil cap the air is probably finding its way through the pcv valve and into the intake

[den7]

Hi, thanks for that input. The fault code was left over from me forgetting to plug in the dizzy at one point . Managed to figure out what the cause was. It turned out to be a rather large vacuum leak. It had a leak in the intake manifold gasket, which must have got worse by pure coincidence... So will replace that some time this week.
Hope this helps out other people who might come across the same problem...