156 2.0 TS Big Flat Spot

Iv'e just read 'Jerky 156' by 'john333' and am getting deja vu.

I bought a '98 with an obviously blowing exhaust for a bargain price. The test drive showed a big flat spot at 3500-4000 in 3rd and slightly higher in 4th. Driving through it the revs then picked up again. Assumming this was all down to the exhaust causing lean running the car was otherwise sweet as a nut and deemed an easy fix.

One new manifold (£20+£10 delivery off e-bay) and a complete pattern system later it's only marginally better than when I first bought it. It also doesn't rev properly after the big flat spot and seems reluctant to rev, most un-Alfa like behaviour.

It also picked up the yo-yoing idle mentioned in 'Jerky156'. I have performed the 'fix' described by gazza82 of taking of fthe idle actuator and making sure it's set up with the throttle which seems to have improved things but not cured it completely.

I also agree with gazza82 that the device on the side of the throttle body is an 'idle actuator' but I am sceptical about whether it would cause flat spots or even the varying idle when the engine is warm. This is because my understanding of this device is that it's an idle speed stepper motor (as used to be fitted on some carbs). This is purely to keep the idle speed up until the engine warms up at which point the throttle then rests back onto the idle speed grub screw. It receives it's signal from the coolant temperature sensor (via the ECU ?) so should not actually do anything when the engine is warmed up. Failure of the device means difficult cold starting unless you rev the engine.

Also, it can't shut the throttle because of the way it is made, it can only open it and even then at very small throtle openings ie. idle. I deduced all this by 1. Taking the thing to pieces and seeing how it works and 2. Starting the engine and driving the car with the thing taken off the throttle body which made absolutely no difference to the idle problem or the flat spots.

So with that lengthy introduction, can anybody offer any advice on the yoyoing idle or flat spots.

- Lambda sensor has been changed.
- 2 doses of Reddex injector treatment administered over 2000 miles.
- Engine run with MAF taken out of intake made the engine stall and the injector light come on - suggesting it's OK. Aslo thouroughly cleaned.
- New plugs and HT leads.
- New air filter.
- it's 126k but had the cambelt done at 80k.
- Battery very healthy.
- A damn good thrash has been administered after each attempt to fault find but to no avail.

One other thing, the fuel gauge continuously jumped from empty with warning light coming on back to correct reading for several weeks after I bought it. It then stopped ie. now reads correctly all the time ... weird.

I was asked if I was mad for buying an old Alfa. Maybe not then but i'm nearly there now !

Not sure, but you need a new cambelt anyway. Interval is 3 years or 36k miles whichever comes first.

Take it to a specialist, and get them to check that the timing is correct. Could be the reason for the flat spot.

moved to 156 lounge

I'm sorry to here about your sick Alfa mate. I too have similar woos but I at least have the performance from 3000rpm to enjoy. I shall be checking this thread to watch your progress mate, good luck.

Flat spot at 3000 is a classic duff MAF symptom. And its WELL overdue a cambelt change!

Went to Angel Tuning in Troon at lunchtime today. They took a MAF sensor out of the same model car they have and swapped it for mine and said test drive it for a couple of days. I only drove it back to work 5 miles so far but (famous last words) it seems to have had a massive effect on and possibly cured the bouncing idle speed and the crap running over 4k (effect on idle was instant). Iv'e asked them to order me a new one. I'll get the new one fitted and give a better road test report when it's done. That's saved me a shed load of hassle as I was going to launch into changing out the injectors as the next exercise in the fault finding.

Now I must remember not to snap that cambelt. There seem to be loads of 156's in breakers that are perfectly OK but have knackered heads.

If it was my car i would trailer it to a garage to get the belt changed right now! There are so many threads about belts/tensioners breaking at just over the 36k that its not worth the risk (in my opinion!).

Now pulls like a train, restoring my faith that the good vibes I got of the engine when I test drove it weren't just a classic case of 'falling in love with the first Alfa you drive' syndrome. But it still jerks on a steady throttle at 80 in top. See the latest iterations below.

It's also booked in for the cambelts and aux belt on Wednesday.

Stuff done;

New Alfa lambda sensor went in on Thusday and this restored the idle to almost normal and improved the flat spot so you could nearly drive through it but made no real improvement to the the jerkiness on a steady throttle at 80 in top.

New Alfa MAF went in yesterday and this has made the idle totally steady and as good as it has ever been. It also improved the flat spot but not cured it completely. It now feels like the traction loss traction you get when when accelerating over a pot hole. But most importantly there is no differerence to the jerkiness on a steady throtle.

With the car running like this I took the idle actuator off the throttle body and tied it up. This is with the electrical connector still in place so the system sees no change to anything. The engine cooled off in the time it took to do this and just as you would expect if the idle actuator was working - it took lots of throttle blipping to get the thing warmed up enough to idle properly. Good. That proves the cold start bit of it works. Now for the test drive. Yes you guessed it. No change to anything at all apart from a tendency for the idle to go very low a you come up to a junction and then it' hunts a bit. But again this is good because it suggests that the bit that is supposed to keep the revs up as you dip the clutch is also working. I also squirted through the idle actuator stepper motor with contact cleaner and got a dissapointingly small collection of what looked like iron filings (fragments worn off the brushes ?). The idle returned to normal after I re-fitted the actuator but there was no improvement in the jerkiness on steady blah blah etc.

So, although I find it plausible that another purpose of the idle actuator is to stop the butterfly tending to close completely on a light steady throttle, it seems strange that it is working normally in other situations. It also looks very new compared to anything else in the engine bay suggesting that a previous owner has already tried changing it.

Or looked at another way - I have only proved that it's not the idle actuator doing something it's not supposed thats causing the flat spot. It could still be not doing what it's supposed to do (ie. keep the butterfly open) and hence theres a flat spot

So if it is working some times but not others, this would suggest that it's not being told to work, which must be by the the dreaded ECU or by whatever senses that the manifold pressure has dropped.

Way forward ?

Is this where an ECU reset is required ?

How much is Alfa Diag ? What do I need to use it ? Where do I get the stuff from ? How much does it all cost ?

There are four pressure tappings in the manifold just after the throttle valve ? Looking from the throttle inwards they are;

1. Top left - soft rubber pipe goes to a non-return valve and then to the rocker cover and then into the air intake pipe downstream of the MAF.

2. Top right - a hard black plastic pipe which goes into the bulkhead in front of the driver. Is this going to a pressure transducer for the ECU ?

3. Bottom left - soft rubber pipe goes back into the manifold about 8" further into the manifold.

4. Bottom right - directly into what looks like a non-return valve with an electrical connector on the side. The pipe then runs under the manifold and I can't see where it terminates.

2 and 4 would seem to be prime suspects for investigation. Does anybody what the function of each tapping actually is ?

Can you get carb conversions for Twin Sparks ? Only joking ha, ha !

Some progress finally.

Cam belts and drive belts done - can now thrash test with confidence.

Iv'e noticed an escape (or inrush) of air from (or to) the petrol tank at each fill up for some time. Not knowing how the breather on a fuel injection car works I have never really thought anything of it. That was until I noticed a distinct banging coming from the petrol tank just as the pressure/vacuum was released !

So I tried disconnecting the blue breather pipes in the engine bay again - it made no difference to the imploding petrol tank. Convinced I was onto something I traced the fuel/breather lines to the connecters underneath the tank (just in front of the drivers side back wheel) and tried again. RESULT - no escape or inrush of air when removing the filler cap after a test run. The blockage or trapping of the breather must be between the tank and the bulkhead. Hesitation on a steady throttle almost non existent and flat spots almost eradicated. Still doesn't rev freely from 5-7k very well but surges again distinctly at 6.5 - 7k. This is after several hundred miles road testing and so is nearly confirmed as a positive result ...

Suspected reasons for remaining unwillingness to come on cam are;

- If theres something trapping the breather it could also be restricting the fuel flow (both flexible pipes ? TBC).
- The fuel pump may be damaged from sucking against a vacuum for so long. Pricing one from a breakers ...
- When I first got the car the jerks were so bad they made the injector light come one. These may have put the ECU into 'get home' mode and all efforts to do the full reset have not made any difference.
- Variator may be goosed. I will be livid if turns out to be true after the garage who did the cam belts 2k ago said they didn't think it needed doing.

Anyway, happyish for now as that yet untraced block or trapping of the breather perfectly explains the apparent randomness and severity of my glitches with weather, journey duration, volume in the tank etc. ie. I was not going mad after all.

I spoke too soon again.

Jerkiness still there at 3250 rpm in 4th and 5th. Time to return to a datum and take stock of the situation.

All blue breather pipes re-connected - no difference. Although running the car and then dis-connecting a coupling produced no sign of any pressure or vacuum in the line (see tip from Doc G on Kangarooing 156 - now desperate).

Is your variator working? Theres the variator solenoid that I believe can be electrically disconnected to see if the variator is working - DOnt trust me though ask someone more knowledgeable before doing it! Usual disclaimer of course.

I think your right about the variator solenoid. On top of the cam cover theres an electrical connector which goes into a solenoid/plunger which goes into an oil way. It seems to be right over the inlet cam (offside). If I disconnect the plug, the engine dies suggesting the variator is OK. 2 screws to take it out and you can put 12 V on and watch it click in and out (or not). Thanks for the tip, I had wondered what was going on there. This may be a test for the variator being faulty but it also may just disable the variator ? Any thoughts from the panel ?

I'm still convinced that my stuttering is a fuelling/air leakage problem. It's fine on and off the throttle - it's just holding 3250 rpm in 4th and 5th on a steady throttle (60 and 70 mph ish) ie. legal cruising (which we all have to do in this camera neurotic modern world) that's a pain.
I'll be checking out the fuel cap and EVAP can tonight. Thanks again for the tips.

Originally Posted by rt05492

I think your right about the variator solenoid. On top of the cam cover theres an electrical connector which goes into a solenoid/plunger which goes into an oil way. It seems to be right over the inlet cam (offside). If I disconnect the plug, the engine dies suggesting the variator is OK. 2 screws to take it out and you can put 12 V on and watch it click in and out (or not). Thanks for the tip, I had wondered what was going on there. This may be a test for the variator being faulty but it also may just disable the variator ? Any thoughts from the panel ?

I'm still convinced that my stuttering is a fuelling/air leakage problem. It's fine on and off the throttle - it's just holding 3250 rpm in 4th and 5th on a steady throttle (60 and 70 mph ish) ie. legal cruising (which we all have to do in this camera neurotic modern world) that's a pain.
I'll be checking out the fuel cap and EVAP can tonight. Thanks again for the tips.

The lightbulb has just come on EVAP only activates under constant revs and if your EVAP is letting in pure air rather than nice fuel vapours...??? Wheres gazza82 when you need him, he is well experienced in trials in this area.

It may be worth investing in a cable and Alfadiag it could help with the lambdas etc.

Oh forgot to add have you cleaned/replaced the PCV valve, part PCV 71713715. Its about £3. CHeck out gazza82 idle saga on his site to see if its worth a go. It didnt work for me. PS I broke mine and had to glue it with superglue trying to remove it to clean it. Its less stressful to order an original from the stealers at £3. Its located just after the throttle body on the manifold and lets air in from the rocker cover once the vacuum is at a certain level.

Originally Posted by rt05492

Went to Angel Tuning in Troon at lunchtime today. They took a MAF sensor out of the same model car they have and swapped it for mine and said test drive it for a couple of days.

Fingers crossed you get get your car running sweet quickly, but that was damn good service from Angel Tuning, a lot of garages would have taken your motor in to test the MAF sensor themselves, charging you handsomely for the priviledge of course!

erratic idel is very comon, replace the idle speed controller (blakc plastic thing on back of throttlebody) mine cost £10 from a scrap car and fixed it instantly.

Just to recap.

I no longer have any idle problems - when I did have, taking the idle actuator off the side of the throttle body made no difference to the idle problem or the faults that as still present as below. Same for new Alfa PCV. See list of other things done earlier in the thread.

Mine kangaroos/stutters/hesitates from 3250 rpm especially on a steady throttle and is reluctant to rev from 4.5-6.5k when it suddenly surges again to 7k+.

Most likely causes are the variable inlet manifold - but mine cycles up and down when the electrical connector is unplugged and plugged back in and is getting good vacuum.

The variator has to be next on the list. I have reached the end of thing I can change/fiddle without having access to Ed China's garage and have therefore booked mine in for a Bosch diagnostic.

I will pass on what comes of it ...

Originally Posted by Rockhopper

Flat spot at 3000 is a classic duff MAF symptom. And its WELL overdue a cambelt change!

It's more like a classic lamda probe problem in my experience.

Originally Posted by rt05492

Mine kangaroos/stutters/hesitates from 3250 rpm especially on a steady throttle and is reluctant to rev from 4.5-6.5k when it suddenly surges again to 7k+.

that screams MAF to me. have you tried driving with its connector unplugged to see if you get power back above 3000rpm?

Lambda already done - no difference.

MAF already done - slight improvement only.

OK - I now have the fault codes off the ECU and they are ;

P0340 Camshaft Position Sensor Circuit Malfunction
P0336 Crankshaft Position Sensor A Circuit Range/Performance
P0325 Knock Sensor 1 Circuit Malfunction (Bank 1 or Single Sensor)

Any advice on where these things lie on the engine and how to get at the plugs and wires to do resistance checks and then get them off/out ?

I have also ruled out the variable inlet manifold - it's not stuck and it cycles up and down when powered up.

I also tried removing the MAF plug but the car won't even pull away without dying ? The car works perfectly below 3000 rpm with the MAF plugged in ? I am struggling with the logic of taking something off the engine that makes it work properly and expecting an improvement in anything ? Surely the logic is that if you take it off and it makes no difference it could be the thing at fault ?