High idle regardless of whether it is cold or hot

[dell_mare]

Hi to everyone! I'm new one here and first apologize for my english. (no blame,you most welcome)
Many useful information draw my attention when I tried to find solution for problem.

I have Suzuki Vitara 1995 1.6 16V, convertible, 178k km, MT, 4WD, built in Spain.

Engine have installed liquid petroleum gas which goes directly to airflow tube and on the same injectors as petrol. Usually people here install liquid petroleum gas (LPG) (0.6 USD/per liter) because it's twice cheap then petrol (about 1.2 USD/per liter).
When I bought it two months ago, fuel system was crappy and dirty. (what fuel system the old petrol or new LPG)? petrol system was crap..gas is upgraded and attested so it works perfectly.
Engine shaked and got this ups and downs when idle running on petrol (1100 to 1800 rpm). He didn't have power to climb up some steep hills etc.
first off doing this to any EFI system this dumb is not easy at all.
The ECU goes to limphome and spark is retarded for ever, ,bad bad that.


When it's on LPG idle speed was normal (around 800 rpm) and got much more power than on fuel. It is very common problem here with dual fuel system (DFS) cars, because engine don't run much on petrol so whole system get rusty and stuffy. So I decided to fix things up with fuel system, low RPMs, gain more power, low consumption etc
oh boy, you want to bounch back and forth between 2 radical different fuel sytems
sure and now the petrol side is bad, injectors packed with junk, they have 10 micron screens that just hate junk there.


Zero step - Fuel pump changed

First step - ultrasonic cleaning of injectors > result: some 20% better performance when accelerating and stabilize idle speed without ups and downs (on LPG > 800 rpm, on FUEL > 1200 rpm). So, didn't solve problem with high idle rpm on fuel.

Second step - changing spark plugs (NGK) and fuel filter (JAPANPARTS). > result: beast reborn - much better performance on the road driving on both systems (fuel and lpg). Still have problem with high rpm's on petrol.

Thirds step - using EGR spray to clean airflow and EGR and physical cleaning of throttle. So throttle was dirty (black fat like things in)> result: maybe some gain of performance but now engine goes way to high even on LPG.
RPMs on fuel - around 1800 (hot and cold either), on LPG - 1000 (hot and cold either). LPG has it's own idle control valve and can easily switch to lower rpms but I still have problem with fuel.

Now i doubt on two things that pushing ECU to idle so high:
- vacuum - false air (don't know how to solve that) I do but never on LPG you mean, LPG want run if there is a problem with vacuum - false air?
- some of the sensors (MAS, ICS etc).

Did someone had similar trouble? ( sure fast hot idle problems, endless ) and cures for all. on PETROL only.

Did you mean driving only on petrol is cure for all?

the 16v ECU is a MAF based fuel system called AIR DENSITY SYSTEM.
The maf tells the ECU air flow and the ECU then calculates fuel rates.
The ECU watches RPM and temp. and controls hot rpm all the time, on petrol. with LPG the ECU will go nuts, totally nuts. so I will not talk about LPG ever. Ok, that's for sure, everyone complains that LPG ruined they petrol systems.

just fuel or petrol. (gasoline here its called and same) Apologize for that - petrol.

dual fuel cars are fully engineered, your is not 'hacked, (no lie there are great LPG systems and too many to imagine, ) but not with fuel. petrol legacy there.

my guess on fuel , RPM failures:
the ISC is dead. it can't control RPM at all, due to TV set wrong. or ISC jammed. open.
HOW I find this is ,
make sure the IAC below the main throttle body had hot water flowing there 82c and is not blocked, if it stall there the IAC sticks open,
IAC is closed 100% 65C and higher. (its a thermal device only for idle are flows)
the ISC on the front left plenum box, is electic and 100% ECU modulated. (non thermal)
it must not stick . either one,
ISC if its duty cycle is seen at 100% on scan tool that means (or 0) that means there is air leaks, or TV stuck open .
The TV plate on this car is 99.99%closed, at all times foot OFF the petro, right foot pedal.
if not its been hacked some way, only 3 things control idle speeds never TV, its closed
TV is closed 100% (.005" open is zero open)
IAC closed hot.
ISC modulating at 50% hot idle scanned, if not set bleed to 50%
that air bleed screw set correctly. Thank you very much for this elaboration. I'm not sure that I'm the man for doing all of these checks and repairs. I will go to one of my local mechanics.

It is real hard to fix OBD1 cars lacking a scan tool
OBD1 cars have very punishing , limphome mode, if you try to fool the ECU. like LPG can,
a good LPG system would replace fuel and spark i bet yours dont run custom spark does it.

THE OBD1 limphome retarded spark is horrible, and way less in 1996 and newer here at OBD2 changes.
Know to that spark advace is 3D, not simple on EFI. its based on RPM AND LOAD.... (and mode, if in limphome , its bad)
we get up to 40 degree's advance (sparK) if working right. and never in limphome.

Today I tried something. Just put my hand in way to shut air intake and see how will engine react. Rpm's got down immediately Is there any solution in checking some kind of dirty in MAF or buying new MAF (even if I saw your comments about cloned MAF)? There is one https://www.aliexpress.com/item/Factory-...81260.html