[BJPK]

in my girls vit g16b its started idleing roughly after a long trip
its not a misfire just rough idle almost like its hunting or similar.
no other problems not hesitating while accelerating etc
thought most likely thing would be dirty iac valve but it isnt that
no vacume leaks that i can see or hear
doubt that its tight vaves or similar as it does it when cold or hot.
ideas please???

[hooki]

I would have geussed a vacume leak, happened to my sierra yesterday. It turned out to be a vac line going from the air box the manifold. Maybe the ecu is in limp mode??

[BJPK]

pretty sure it would throw a code if in limp mode, also uaually a limp mode limits top speed etc.

[waimser]

Yeah I just read a but load of limp mode stuff and it deffinately limits rpm and power.
Id check the egr system is working right. seems the cpu is very dependant on it and rough idle is an early symptom.

[BJPK]

come on guys any oyher ideas?

[nissvit]

is it hunting or is it rough?

if its hunting have you recently checked the idle speed and the duty cycle of the ISC valve?

if its rough have you checked the simple stuff?? ie leads (particluarly no 3), plugs, & scraped off the oxidisation build-up on the terminals on the inside of the distributor cap.

[BJPK]

running rough. not misfiring though.
going to give it a major on the weekend fuelfilter, plugs, check dizzy cap etc.
but if it were leads or cap id assume it would misfire under load.
only other thing i can think of is dirty injectors, possibly a bad spray pattern at idle but still disperse enough fuel under load to avoid a misfire?

[steak_knife]

BJPK wrote:

pretty sure it would throw a code if in limp mode, also uaually a limp mode limits top speed etc.

My car's in "limp home" (eng light on) & it goes like a shower of stuff..

If it has a limp home it doesn't make it run rough.

[nissvit]

what year is the car, does it have a three or five wire air flow meter.
there was someone on here who's old style AFM stuck open and caused mixture problems at idle..

[BJPK]

nissvit wrote:

what year is the car, does it have a three or five wire air flow meter.
there was someone on here who's old style AFM stuck open and caused mixture problems at idle..

its 96 pretty sure its the 3 wire one. i sprayed the hotwire with throttle body cleaner. but couldnt see a flap in it? vehicle isnt here now so cant check.

[LAY80N]

Dont use throttle body or brake cleaner on hot wire AFM's, it leaves a residue on the wire. Use electronic parts cleaner, it dries clean.


Layto....

[BJPK]

LAY80N wrote:

Dont use throttle body or brake cleaner on hot wire AFM's, it leaves a residue on the wire. Use electronic parts cleaner, it dries clean.


Layto....

thats the stuff i used electrical cleaner.
pretty sure it got a burnt exhaust valve on cylindar one.
as when i pull the leads off one by one this is the only cylindar that doesnt run any rougher.

[JrZook]

BJPK wrote:

LAY80N wrote:

Dont use throttle body or brake cleaner on hot wire AFM's, it leaves a residue on the wire. Use electronic parts cleaner, it dries clean.


Layto....

thats the stuff i used electrical cleaner.
pretty sure it got a burnt exhaust valve on cylindar one.
as when i pull the leads off one by one this is the only cylindar that doesnt run any rougher.

Have you checked the plug on that cylinder yet? Does it spark? Do you have compression on that cylinder. How do you determine that its got a burnt exhaust valve just from pulling the lead off and noticing that the engine doesnt run any rougher?

[Ben_Sierra]

JrZook wrote:

BJPK wrote:

LAY80N wrote:

Dont use throttle body or brake cleaner on hot wire AFM's, it leaves a residue on the wire. Use electronic parts cleaner, it dries clean.


Layto....

thats the stuff i used electrical cleaner.
pretty sure it got a burnt exhaust valve on cylindar one.
as when i pull the leads off one by one this is the only cylindar that doesnt run any rougher.

Have you checked the plug on that cylinder yet? Does it spark? Do you have compression on that cylinder. How do you determine that its got a burnt exhaust valve just from pulling the lead off and noticing that the engine doesnt run any rougher?

x2...

You've narrowed it down to a cyclinder, but there are plenty of other things that could be wrong on that cylidner...

[BJPK]

its not a burnt valve carried out a cylindar leakage test.
also tested compression wet and dry and its low on cylindar four but this doesnt explain the rough running on cylindar one. checked valve clearance ok, tested leads all ok. swapped over another ditributer cap still not fixed. dont think its injectors as it runs rougher when they are pulled of individually. pcv not blocked, iac valve is ok. unless its jus running rougher cause it doesnt have enough compression on cylindar four??
still doesnt explain why it doesnt change when lead one is pulled off yet it runs really rough when lead 4 is pulled. a little confusing to say the least.

[Ben_Sierra]

If it doesn't change when lead one is pulled off then that would indicate that cylinder one isn't firing for whatever reason...

Now you just gotta check everything to do with that cylinder!

[BJPK]

Ben_Sierra wrote:

If it doesn't change when lead one is pulled off then that would indicate that cylinder one isn't firing for whatever reason...

Now you just gotta check everything to do with that cylinder!

theoretically yes but it is firing good spark. and has fuel and compression is ok and valves are sealing so should run rougher when the lead is pulled and spark stops but it doesnt. cylindar 2 runs slightly rougher when the lead is pulled but 3 and 4 run very rough when pulled. going to run a few bottles of injector cleaner through it, possibly has a bad spray pattern at idle. see how we go.
it is possible that that cylindar 4 has always been low on compression and is unrelated to the rough idle/miss. yhe only other thing i can check is tps highly doubt it would be at fault though.

[steak_knife]

Pull the fuel rail up, swap no's 1 & 2 injector's, see if the fault follows..

[Spooky]

Hey Nissvit, you mentioned that BJPK should check his No 3 lead. Why this lead in particular? Mine has a rough idle sometimes but clears itself with a few revs.

[BJPK]

steak_knife wrote:

Pull the fuel rail up, swap no's 1 & 2 injector's, see if the fault follows..

going to check the fuel rail for pressure and then pull the injectors out and send em out to be cleaned will post results when done.

[nissvit]

Spooky wrote:

Hey Nissvit, you mentioned that BJPK should check his No 3 lead. Why this lead in particular? Mine has a rough idle sometimes but clears itself with a few revs.

in the g16b's in a vit, no 3 is directly under a bracket that holds the air intake pipe. my theory is as it is hard to pull up evenly the lead gets damaged when people change plugs..
In about five g16b's I've worked on, no three lead has been damaged..

[SSSIERA]

LAY80N wrote:

Dont use throttle body or brake cleaner on hot wire AFM's, it leaves a residue on the wire. Use electronic parts cleaner, it dries clean.


Layto....

mortein. dose the same trick. and leaves no residue.... bit cheeper to