Stuttery Revving :)

[Chris_C2000]

I orginally posted this in the GTV forum but not much response so I thought I'd move over here

1997 Phase 1 GTV, 2.0 TS.

Right.. I'm not sure if this has been there for ages and getting worse slowly or if I've just not paid enough attention and something I've done recently has caused it..... I've only had the car for 4 months and am only just started learning to do anything mechanical with it (I dont think you can own a GTV and not be at least a part time mechanic unless your very rich!)

Anyway...

Revving the engine the rev counter jerks upwards, every 500rpm or so (Depends on how fast you rev it), the needle jerks for a just noticable moment and then continues.. also does it on the way down as well.

It does not seem to be affecting the performance *that much* but I have nothing really to compare it to.

MAF has been replaced with a 'known good secondhand' one from someone on here, disconnecting the MAF makes the stutter worse if anything.

Work Done Recently :

MAF Replaced
Cleaned throttle body
Resonator Box on the air inlet replaced with a length of drainpipe.
Cam Cover Gasket Replaced
Oil Change (10W-40 put in to replace the black gunk that was in there)
Exhaust Mid section has a small hole in it.. patched with a clamp on patch but possibly not that tightly.
Air pipe has been throughly checked and has no splits
Air Filter box *is* cracked on one side where some gorilla has snapped off the top half of the bracket, trying to source a replacement.


After some testing (read driving too fast) today I've concluded you can hear it in the engine too.. 1st/ low 2nd not so much, same with 4th (it's there just not really noticable) however higher in 2nd and all the way through third when driving hard (acclerating foot to the floor) you can hear the engines not smooth it's going kinda.. vuv.vuv.vuv (read it out loud fast ) if that makes sense.

Now I could be being a car hypercondriac and everything is fine. However I learned my lesson with the thermostat and even the smallest things can make a big difference so I would like to be sure

[Chris_C2000]

Ok and now on the way home it's hunting (well wobbling slightly) when driving along steadily. Ie. At a steady 70 you can feel and see the rev counter *just* wobbling up and down quickly.

Edit : Idle is steady, it's always hunted a little on startup (for 5 seconds or less).

[Dr GTA]

Sounds like your throttlebody needs a clean. You need to be vary careful with it as its very fragile. Use electrical contact cleaner but be light as a feather if you have to touch it.

[Dr GTA]

it could also be your air flow meter on the way out, but that normally is just a loss of power.

[gazza82]

I don't know if the GTV is like the early 156, but the chances are you have slightly upset the throttle body idle actuator. This is a black box mounted on the right side as you look at the throttle body. Assuming that you also have a throttle cable. On the 156 you can reset this by turning on the ignition for 90 secs, turning it off for same time and then starting the engine without touching the throttle pedal. Leave it to idle for 3-5 mins and it might improve. Otherwise you may need to have to get the actuator reset on a diagnostic (Alfadiag, FiatecuScan or Examiner at the dealers, who will charge).

The problem I found when mine was out was that we couldn't hold 2,500 rpm using the throttle pedal. The rpm's would dance up and down even if you wedged something under the throttle pedal so you couldn't move it. Makes the emissions test on the MOT almost impossible to pass.


Hint for anyone considering cleaning the throttle body: take the throttle off and remove the idle actuator first!! There is a plug underneath which is easier to remove if you undo the throttle body from the intake and turn it through 90 degrees.

Replace the throttle cable FIRST, then the actuator holding the butterfly shut, then refit the body to the inlet manifold. Otherwise you can get the actuator out of sync with the ecu as you pull the throttle open and closed to get the throttle cable back on.

[Chris_C2000]

Ah-ha!

That seems to have sorted it (or at least 95%!) went out for a short burn after the procedure above and it was wildly improved. Couple of hiccups at different times under hard acceleration but nothing like as bad as it was before Thanks Gazza!


I tried to remove the actuator to give it a clean as per other threads in the GTV forum (ie. blast of carb cleaner and very gentle with anything else). But it was done up a tad tight and I've slightly rounded off the ribe screw/bolt things. Will give it a dose of WD40 before trying again.

[Chris_C2000]

Hmm.. started off right after the reset last night amazing.. been getting slowly worse over the next 40 miles.

Idle Valve on it's way out??

[gazza82]

Have you got (or can get access to) AlfaDiag or FiatEcuScan. They have an "Idle Actuator Reset" feature which is worth trying first. Also check the connector on the underside of the idle actuator itself.

[Chris_C2000]

Originally Posted by gazza82

Have you got (or can get access to) AlfaDiag or FiatEcuScan. They have an "Idle Actuator Reset" feature which is worth trying first. Also check the connector on the underside of the idle actuator itself.

IF I can get the bloomin thing off without destroying the soft as butter ribe bolts