20v Silvertop Idle fault

[MikeWolf]

Hi,

For the last 6 months or so, i've had an idle fault with my 20v that I can't seem to diagnose. When it starts cold in the morning, it idles around 1500-2000rpm, and then drops to ~1000 when warm.

Trouble is, when i'm crawling through traffic, constant stop go etc) the idle speed becomes erratic, dropping very low (~200) when I take my foot off the gas and then recovering after a bit of a struggle. If I keep this up long enough (1 hour crawl to work in the morning, Auckland traffic ftw), it will drop and then simply die, instead of recovering.

I've also noticed it pings very easily, and gives a fair bit of grey smoke if I thrash it. So far i've tried:

New ECU (borrowed from a mate's working AE101)
New dizzy cap + rotor (were very worn)
New thermostat + O2 Sensor (both were dead)
New Airflow meter (again, borrowed from friend)

None of which made any difference at all.

I've had someone suggest that I check the TPS, but I don't know how, and i'm told it's not something to mess with if you're clueless. I have a workshop manual, but I can't find anything in there about testing/adjusting TPS.

If anyone's got any clues as to what could be the problem, i'd really appreciate some help with this one. I'm seriously debating selling and purchasing a rather mint GT4, but i'd like this to be in good condition for when I do. Cheers!

[Mr Revhead]

what grade gas/brand of gas?

[MikeWolf]

Premium (depends where I am when the gas gets low), if I can I try to use BP ultimate or Gull premium.

[KinLoud]

I know of a similar problem in a 20v silvertop.
Turned out it was one of the rubber hoses from the intake to the power steering that help control the idle up had come loose.
Have a good look from above and below as these hoses can be hard to see and trace.

Ken
Ham
021 408 863

[MikeWolf]

All have been checked, no problems there.

[MikeWolf]

Is anyone able to post a quick description on how to test ISCV + TPS? Two things I haven't been able to check yet, would be greatly appreciated...

[MikeWolf]

Anyone got any ideas? I'm desperate for help with this. I'm selling the car soon to buy a GT4, and a problem like this would seriously hinder the price I could sell it for. Many thanks.

[Caveman]

FAQ section

http://forums.toyspeed.org.nz/viewtopic.php?t=29042

Check all vaccum lines, they can appear fine but may have splits in them or be broken around the fitting.

[MikeWolf]

Ok, i've noticed something odd.. when my engine is warm/hot (which is when i'm having my problems), the throttle stop screw doesn't contact the stop (which makes doing anything with feeler guages rather futile). Is this normal? Or do I need to mess around with the TPS?

[Mr Revhead]

iirc theres a vacuum operated pushrod that opens the throttles slightly for cold running.
sounds as if thats opening when it shouldnt be.

have you checked both the temp sensors?

[MikeWolf]

Forgive my noob-ness, but 2 temp sensors = IAT Sensor + Water temp sensor?

[Mr Revhead]

water temp sensor for coldstart switch on the back of the thermostat hosuing point forwar
and sensor for the EFI on the top of the housing facing down

above locations are off the epc, but iirc the EFI one is on the gearbox end of the head.
cant remember exactly at the mo!

[sergei]

A few corrections (for 20v in FWD):
1) pushrod inbetween #2 & #3 throttle is connected to dashpot - the purpose of it to keep throttle open for short amount of time (and gradually close it) when accelerator pedal is suddenly dropped.
2) cold and hot idle is controlled by idle control valve which is located on the head below #4 throttle.
3) looking at the engine from the front of the car: white 1 wire plug on the thermostat housing pointing towards left of the car (gearbox side) is thermo switch for radiator fan. The green sensor with 2 wires, pointing up, located on top of the thermostat housing and very close to head is Water Temperature Sensor for EFI, finally the last sensor with blade type of connector, pointing towards rear of the car and located behind the thermostat housing is for temperature guage in instrument cluster.

With that high idle and random rpm drops while hot, check your ignition timing as too advanced will result in high idle on cold/warm but when it gets really hot it might retard ignition too much and result in stall.
The screw on AFM is NOT for idle adjust. You cannot adjust idle on 20v (easily) due to each throttle has got individual idle adjust screw which is accessed from inside the plenium. Check if your idle control valve is not full of oil/gunk. To clean you have to remove hoses from it (they are about 20mm in diameter) and soak it in CRC/Carb cleaner, and blow it out with compressed air (very carefull from distance as it is possible to damage mechanism inside if it is not done right).

[sergei]

Also, long time ago I had dodgy injectors in my 20v. it would cause black smoke on average load (diesel style), also it would have erratic idle, detonation, black spark plug tips, while A/F readings would be normal, and fuel economy was ok aswell (although I started to get much better economy straight away when I replaced the injectors). The injectors from facelift are different from items on prefacelift silvertop. The holes are spaced diffferently. As far as I know most of the prefacelift injectors will cause black smoke problem (I had about 6 sets of them, only 2 sets of facelift ones were ok. I tryed soaking insides of the prefacefilt in aceton with no luck).