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Hey tuners I need some advise if anyone had this issue before. The engine is a QG18de. When cold the engine starts and idles great. It warms up, reaches operating temperature and still idles good I would average between 950-1000 rpm. I can use the car on normal driving for most of the day with no issues. I have also left the car idling for a half hour and no issues. The problem is once I do some WOT pulls with the engine I get good power and top end but once I slow down and the engine reaches back down to say 1200 rpm it stalls. Once it does this and I restart the engine would not idle. I have to let the engine cool down a bit and then it would idle normal again.

The engine check light does not come on when it stalls so i ran checks on other areas that may cause the engine to stall. So far I took out the throttle body and injectors cleaned them properly put in new plugs checked all the vacuum lines for leaks. The air filter is clean and the fuel pressure is good. I dont know the exact fuel pressure because i dont have a guage but everything seems to be ok. The car revs and pulls off rel hard even at operating temperature but with a few WOT pulls the car just stalls when returning to idle.

I've been doing some research and most of what I checked already are the suggestions to fix the problem so I need some more suggestions. I also came across some people saying vapor locking in the injector rail after a hard pull may be an issue but I have no idea how to diagnose that.

Any suggestions would be great because I am currently rechecking everything in the engine.

did you check the idle sensor
and the tps sensor?

I cleaned the idle sensor. But did not want to interfere with the tps.

Did another diagnostic and nothing showing up.

check the IACV - idle air control valve. also the QG18 is supposed to idle @ 750rpm. 900 is a bit too high. on the underside of the bonnet there is supposed to be a sticker- check an verify

also check the air flow sensor...clean it and reinstall.

you didnt specify which Qg you got. cable throttle type or electronic throttle type.

Cable type qg18. Cleaned all IACV already.

Cleaned the air flow sensor also.

Just checked back everything. Throttle, sensors, plugs, coils, and I changed all the vacuum lines. Carried it for a WOT run. Ran one mile rel hard and when I slowed down car stalled. Restarted and it would not idle. I let it cool a bit for a ten minutes and it began to idle properly again. This problem is very frustrating

try this - start the car and let it idle - let it get up to operating temp on its own - then hold the car at one RPM example 2300rpms- does it fluctuate on its own??? ie rev up and down even though your foot is one constant pressure on the pedal??

Tried it, the rpm holds steady at varying points too. Held it at 1500, 2000, 2500, 3000 engine runs steady where I hold the pedal.

you said it would not idle... what exactly happens - you turn the key and the engine doesnt turn over-?? it idles super fast like 1200 rpms and more or idles really rough.??

have someone check the fuel system- pump and lines. it may also be the IACV playing the a$$

It starts and idles good, reaches operating temperature and still idles good even if I'm revving it hard at stand still. The idling only goes to sheit right after I make a hard WOT run, as I slow down the car stalls.

And once the car stalls when I restart the engine it just starts and cuts off. I have to let it cool a bit and then it would start and remain idling.

Will run some more checks on the fuel pump and lines tomorrow. Hopefully I find what's causing it to stall. Will also see if I can run another diagnostic.

engine stalling on a rapid decel..is an indication of an iacv prob....do you have any hole in yuh muffler..
air is getting in

Will see if I get another iacv tomorrow and try it also.

when you doo a diagnostic on an issue like this you wont get codes....you must know the values of the tps,,,throttle...maf sensor... rpm level ....etc etc// then with this knowledge you will spot a value that is wrong....for example
at idle your---RPM= 750 at wide open throttle rpm = REd line on tachometer
TPS =.5 0F A VOLT Tps = 4 volts to 4.5 volts
Absolute Throttle = 0% Absolute throtlle shold be close to 100%
Maf = aprrox 1,25 volts Maf should be over 4 volts
Iacv = approx 20% Iacv should be high close to 100%
O2 sensor shoukd fluctuate O2 sensor should stay at a high value on WOT
.12-67,,22-76,,,33-69 etc .77-86,,75-89..etc....if when you decel it goes low
quickly there is a lean condition...either too much air
or too little fuel
these are some of the values at idle..and wide open throttle..hope it helps

coolant sensor
crank/cam sensor
spark plugs/ring oil seals

Got through tuners. Check engine light finally came on yesterday and it turned out to be the crankshaft sensor and knock sensor. Changed them and cleared the codes and so far the car is running good.

your welcome