Surging idle

[scalpel]

Hey,

So i been having this erratic surging idle
And i thought after i cleaned my throttle body and replaced the aux air valve/iacv that things would be good

Nope. It still surges. Idling screw all the way down.

Also changed fpr from a non stock back to stock

I dont know if it is a bad tps?

All the other egr vaccum lines are plugged

[totta crolla]

Is this an engine conversion or did the car come with installed engine from the factory? If it is factory then it could be the TPS. Try doing a diagnostic test and report results.

[scalpel]

This was a conversion.
Sr5-> gts

But all gts and everything was working for months and then all
Of a sudden one day atarted surging

[jondee86]

Do both of the small coolant hoses connected to the AAV get hot (like as hot as the top
radiator hose) when the engine is up to temperature ? If only one gets warm and the other
one stays cool, there is a blockage that needs to be cleared.

Cgeers... jondee86

[Nick94tt]

Oddball chance, but one of the lines running to the iacv may be clogged as well. Would explain swapping iacvs having no effect. Could disconnect the hoses and spin the water pump by hand/bump the starter - see if it pushes any water out.

If I remember right - won't a failed/disconnected coolant temp sensor cause a surge? (Might just be a high idle - been a while)

[scalpel]

Totta- thanks for the reply
Jondee- I'll check
Nick- thanks may replace the coolant temp also unsure if just high idle vs surging

Would the coolant lines to iacv still be an issue if I had a new radiator installed recently and new coolant etc (koyo rad)

Friend thinks it could also be TPS gone bad

[totta crolla]

It could be that the TPS needs setting again. There is an idle switch in the TPS that must be engaged when idling if the switch is not engaged the fuel calibration from the ecu is wrong. This is relatively easy to check for free and the best way I have found is first to accurately scribe the current TPS position (so you can return to this setting) warm up the engine and allow it to idle, now you turn the TPS to see if the idle gets better. If it does then you have probably just engaged the idle switch.

[Nick94tt]

Would the coolant lines to iacv still be an issue if I had a new radiator installed recently and new coolant etc (koyo rad)

Same way you can swap a radiator and still have a clogged heater core - the iacv coolant lines are much smaller though. If nothing flows out of them when they're disconnected and the water pump spins they may well be clogged. My understanding is they see a constant bypassed flow so they don't rely on waiting for the whole car to warm up enough to open the thermostat. No flow = clogged somewhere.

Easiest way to check is what jondee suggested. Get the car to full temp and feel the lines, they should both be hot. If not, flow problem somewhere.

I'd have no issue trying what totta suggested at the same time btw. Easy check.

Also, remember wires and connectors tend to die before sensors on older toyotas. (My experience anyhow) Outside of the TPS and AFM/MAF units at least. Simple resistor type sensors tend to last a long while - and are really easy to test with a multimeter.

At one point I had a phantom idle surge and stall issue I didn't figure out until realizing the retaining clips were busted off the afm and TPS sensors when the previous owner pulled the motor. Another one because they loosely twisted the ignition power supply together and tucked it back into the wire harness sheath without soldering, connecting, or taping...

Keep at it. Plenty of folks here to try and help. ^_^

[jondee86]

... also unsure if just high idle vs surging

To clarify... high idle is when the engine idles at a constant speed that is higher
than normal. Surging / loping idle is a rhythmical increase-decrease repetitive
cycle much like someone gentlly revving the engine over and over.

The commonest cause for surging / loping where the engine revs to around 2000rpm
and then drops back to around 1000rpm is cycling on the fuel cut. Fuel cut is inhibited
by the ECU until the engine reaches a certain temperature, so usually the surging does
not start until after the engine has been running at a high idle for a couple of minutes.

The usual cause for cycling on the fuel cut is the AAV staying wide open because it
is either broken or it is not being heated up by hot coolant from the cooling system.
That is why you need to check that there is no blockage in the small hoses or the
small metal tube that supplies coolant to one of the hoses.

If the AAV is working correctly the idle will be around 2200rpm on cold start, gradually
tapering down to around 900rpm as the engine comes up to operating temp. If your
engine does not do that, your AAV is not working and you need to find out why

Cheers... jondee86

[scalpel]

Nick/jondee thanks

Got busy over the few days will try working on it today



Will update thanks again