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P0172 code, low revs on petrol and lpg,

MrNotEnglish

MrNotEnglish

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Messages
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8
Location
East Cornwall
Car
2.4 i-vtec Ex Auto
Hi guys, I have a problem with my cl9. Everything was fine until when parked, revs dropped down, engine stopped, check engine came up. Started engine again only on petrol, rev'd couple times, exactly the same has happened, started once again and switched on lpg, rev'd and again engine stopped after revs dropped. It's fine when driving and keeping revs above 700revs/min. I drove 10 miles, then parked and checked again- the same sympthoms, but after keeping revs with accelerate pedal they stay where they should, but as soon as I switch off AC engine stops after rev drop (happened on petrol and lpg). It was perfectly fine on petrol and lpg, and even now keeps the power on both. What it could be? MAF sensor or lambda sensor? Air filter replaced about 1500 miles ago, engine oil changed 100 miles ago, ecu remapped by littleboo about 12000 miles ago. I'm going to have valves adjusted next week and lpg check and adjustment done as well.
Because it happens on petrol and lpg I would say that's not lpg injectors or petrol injectors. Have had some problems with starting not far ago, had to turn little bit longer sometimes, but I blame valves clearance that needs doing.

Please help guys, I'm on holiday 1300 miles away and coming back home on 26th so need to sort it out asap!
 
Hi Littlebo, thanks for reply. Tell me please one thing- is it possible that petrol settings in ecu (responsible for idle revs etc) can be affected and values changed/modified by ecu itself due to lpg set and running to different petrol map? I had lpg installed, then remap but lpg map is untouched, will be adjusting it on Friday. For me it looks like due to petrol remap, sensors getting unexpected values because lpg runs with old (pre remap) settings. It looks like it could be few things if I consider sensor fault. MAP, TPS, O2 sensor, Temp sensor. It's not injectors or fuel pressure as it happens on both petrol and lpg. But then should throw up fault code regarding one of the sensors if values go out of range. Or maybe I'm wrong. Thanks
 
Try to remove air filter first or even run a lil with air tube disconnected from Throttle Body and see how it goes. If no changes then disconnect primary o2 sensor connector and see if you have that stall \ rev drop problem. Youll have CEL for o2 sensor but ECU have emergency map to handle everything. Do all the tests on petrol. LPG system is slave system and if petrol mode will work fine then LPG also will be OK like it was previously. Its extremely rare to have dead MAP and if you have faulty TPS then youll have CEL for it. You can also additionally monitor for fuel trims during the problem and if your sensor reading are OK during regular driving.
 
TPS code is P2138, not unusual on 7th gen petrols, & with things being ok above 700 rpm, maybe the resistor is worn out below that.
 
All solved now. I had ecu remap done- petrol map only, not lpg, so when running on lpg values were different that petrol ecu was expecting. I think it was the reason, because I fixed it and now it's fine on petrol. Not sure yet does lpg needs only adjusting or something broke down somewhere there. Anyway, I turned off lpg and shut off lpg valve next to the tank. I disconnected first from right ecu plug to reset idle revs settings. 5 mins later plugged back in, turned on the engine, didn't touch anything, all electronic inside off, no ac, lights or stereo, didn't touch pedals, left it till fan started first time. Then left it for 10 more minutes and it looks like ecu learned idle revs right.
I'm going to have tein coilovers installed tomorrow then valves and lpg adjusted on Friday :)
 
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