G13BB 1999 Jimny Idle Issues

Have an idle issue. Warming engine up seems stable but after driving and stopping at lights the idle stays stable at first but after approx. 1 to 2 mins always variable, the engine idle plummets then comes back up a few times (surging) then stalls. It starts fine and drives quite well. Have no engine performance issue on highway driving.

A prior problem, I recently had it diagnosed with a faulty IAC so replaced that with (non Genuine), the vehicle had improved but used to get occasional idle hiccup but not often. It now does it every drive in the cold weather. So it got worse. Idles ok at times.

Does this sound like a faulty IAC , could have been dodgy as new? TPS? No check engine light. May be a slight power loss but generally feels ok.

Last time the IAC failed there was excessive power loss going up hills, surging on accelerator and deceleration, high idle general bad performance but the symptoms now are not the same, the common thing being the idle fluctuation. Any ideas. Engine has extractors and a high flow CAT. Doesn't give much better performance but engine stays a bit cooler. Probably better acceleration at the 2500rpm onwards.

If I had just seen the symptoms I would have said sticking or blocked IAC.
As it's been replaced it does suggest something else, but unbranded replacement parts can be a bit of a lottery, so it's not out of the question it's at fault. You have nothing to loose taking it apart and checking it's clean and free to move, also check any electrical connectors at the same time.
During warm up it's a different (thermal) control of the IAC, once warm the electrical "stepper motor" type control takes over, so the warm up phase control is different. I am unfortunately basing my suggestion on a Toyota IAC system as I have never had need to touch the Suzuki IAC, but they can't be that dissimilar hopefully.
Good luck
Mike

Had a search on forum, this is a well known problem. Sounds like the IAC and / or TPS. I have another IAC valve (Denso) will try that. Otherwise im leaning towards the TPS after that as they work closely together.

Thanks Mike , were thinking similar. The IAC on these is a electromagnetic little cylindrical type. Yes I agree, aftermarket parts are a lottery, I regret not buying the OEM. I have a Denso one which I will try. Looks like a bit of quality but its about the internal electrics and quality of build. It sounds like a sticky valve in the IAC. Seems it cant adjust to changes needed after a few minutes idle. And it is intermittent which makes it all the more suspicious of some binding going on in that electromagnetic cylinder.

After all that, changed the IAC valve, no joy, idle still deteriorates when engine warms up to operating temp. During warm up and a short period into engine operating temp the idle is reasonably stable, but then it lets go with a stumble, fluctuates from there on. generally it drives fine but the idle is dodgy. I cant say definitely its a coil as it drives well with no spark breakdown, no engine hesitation, how do I isolate a bad coil that is intermittent and only at idle?

Did multimeter test on TPS all within spec. From idle position to full open throttle is less than 1.5 kilo-ohm. difference. And static idle and full open resistances were within spec. Might be a manifold leak but I don't know at this point Ill check tomorrow. IIf theres no manifold leaks Ill hand it over to the experts. Parts changing can reach the big $$$$ fairly quickly. Over here $347 for a TPS, Over $400 for a IAC valve, EGRs over 400, Im being conservative. EEbay is sometimes a bit cheaper but not much for the OEM product.

Prob take it in to the auto electrics place to see if they can isolate the problem. They have the diagnostic gear and scopes etc, but all at a hefty hourly price.

I've just done my IAC valve today ('08 13A) which is a similar setup. I just gave it a good soak and it made a huge difference to low speed drivability. If your problem is just at tickover the TPS is far less likely to be at fault (TPS has an influence across the rev range). Try running the car with IAC disconnected, if there's no difference then the valve isn't doing anything. There isn't much to the electro magnetic part so give that a clean too. I didn't have a 5 point torx so I just cut slots in the screw heads, once you've separated that piece a good clean up is easy. Don't forget to check the throttle butterfly is seating correctly, good luck. Chris