Club 80-90 Forums

I have the same symptoms. I have not figured it out, but it seems so be a combination of problems. First of all: check your CV bolts, mine comes loose from time to time and makes the jumping a lot worse (don't know how that is related, but somehow it seems to be). The other thing o do that seems to be helping is running some (as in a really strong dose) injection cleaner through it. The last thing i do is to rev the hell out of that damned thing Seems like revving it to 4-5000 every time I accelerate will make it jump less at low revs.
Not sure how that could help you, but it seems to keep the problem at bay on mine.

Oh and by the way: I don't take any responsibility for any kind of damage that might occur by doing what I do. What works for my engine might kill yours!

This may be way off the mark but may be worth mentioning.

If you have 'slack' in the syncro drive train your van can kangaroo when crawling in traffic if you have your foot off the gas. Someone far brighter than me will tell you why; but from memory, the 2.1 ecu hunts for the right idle revs; because the van is under load the lack of pedal causes the ecu to increase power, when the revs are met the ecu powers down. This interacts with the slack in the drive train and causes the whole system to amplify to the point that the drive starts snatching and the van kangarooing as the ecu hunts for stable revs.

this is the remnants of a long past discussion I think I had with someone... ....does not explain the problems you are having at the higher rev end; but you may have two unconnected things going on ?

Mudlark wrote:...If you have 'slack' in the syncro drive train your van can kangaroo when crawling in traffic if you have your foot off the gas....

That would explain why tightening my loose CV bolts helps...

CV Bolts are all tight.

In desperation (not having bought any new bits to trial yet) I tried the "Intermittant Vanagon Syndrome" solution of soldering a 25V 22 microfarad capacitor across terminal 2 and 4 of the AFM. Bizarrely it runs like an absolute bag of nails now..... I was assuming I would either have a miraculous solution or no effect whatsoever?

The Temp 2 Sensor was mentioned in a previous post..... is that the Intake Air Temp Sensor in the air flow sensor housing, coolant sensor (syncro specific?) or a different temp sensor altogether?

Might have answered the temp 2 sensor query..... think its the one on the thermostat housing and engine revs rise when I pull the connection so its doing something!

Also snipped the capacitor back off the AFM and it is still running like a pig on stilts so that isn't the problem.

When I started this exercise I had a bit of a stutter or kangaroo at 1800rpm, I now can barely drive the thing across the rev range, losing power as you put your foot down. All I have done is seperate connections, clean with contact cleaner and remake the connections. SO either the problem is deteriorating OR I have caused another problem on top somewhere along the line. Looks like I will be seperating everything for about the 10th time tomorrow night...........

Gone through the meter checks on the ECU connector plug end, seperated and contact cleaned every connection, dash of wd40 on all the terminals, spark plugs all out and checked and put it all carefully back together...............doesn't run at all now!

Have now re broken every connection, resprayed very liberally with contact cleaner to clear the wd40 and had to leave it all to dry out (too dark to see now). Cannot believe that every time I have touched the wiring on this thing it has made it worse

Running again, though still badly! I had managed to break a wire on a crimped connector out of the ignition control module where it had been previously joined.... ouldn't see it in the dark!

I am pinning my hopes on the ignition control module...got one on the way so should know either way once that arrives!

Mate, sorry to hear this is still going on. I can't offer any advice as you seem to of done everything I'd suggest. Next step is as you say...swapping bits in. See what happens. Good luck.

This might be a long shot but my Doka gave me the same problems for a while after I had gave it its regular service.
Went down the Vanagon Syndrome and cable connection, timing.injectors,CV joints etc to no avail
Turned out to be the metal shrouds round the spark plug connecters as once they were removed it ran better than it ever had.

The lead set was Bosch and only over a year old but the difference it made once they were removed was incredible. It was only when I was checking over the AFm meter
connection in the dark after yet another bout of erratic running that I spotted the tracking problem which still baffles me as they never gave me any shocks when I pulled off the HT leads one at a time to check the spark pkugs were not the problem.

Hope this helps........you've just got to keep trying as it will make you a better mechanic for curing it than resorting to a box of matches....................

wasn't the ignition control module even though it failed the diagnositc check ......

decision on what bit to throw away money on next.... temp 2 sensor (next cheapest bit to try!), AFM, coil, hall sender, vac advance unit or something else?

Can't see any spark tracking in the dark so far from the plug shrouds. They are new bosch ones.

Thinking of actually going back to all the old plugs, dizzy cap, rotor arm and HT leads to see what the effect of that is so I've been rooting through the bin in my garage! Will try that tomorrow.

To summarise
It was hesitating and bucking at approx 1800rpm in 2nd gear coming onto the throttle and it could be pushed through the problem by going hard on the throttle. This focussed the attention on the TPS and the AFM.

Now the problem is more widespread across the rev range. It now feels like it loses power if you go hard on the throttle. It hasn't cut out but feels like it might if you don't feather the throttle.

By my following the manual tests kindly passed on to me the only fail seemed to be the Ignition Control Module. Have now tried another which is exactly the same.

Am I missing something obvious .... what shoudl I try next? (I am assured that a box of matches and 5 litres of unleaded is not the right answer!)

Just a thought,,,,,are the plug gaps correct ?

Explanation:: The gap adjustment can be fairly critical, and if it is maladjusted the engine may run badly, or not at all. A narrow gap may give too small and weak a spark to effectively ignite the fuel-air mixture, while a gap that is too wide might prevent a spark from firing at all. Either way, a spark which only intermittently fails to ignite the fuel-air mixture may not be noticeable directly, but will show up as a reduction in the engine's power and fuel efficiency. The main issues with spark plug gaps are:

* narrow-gap risk: spark might be too weak/small to ignite fuel;
* narrow-gap benefit: plug always fires on each cycle;
* wide-gap risk: plug might not fire, or miss at high speeds;
* wide-gap benefit: spark is strong for a clean burn.


Regards


Fritz,,,,,

This fault may not show up straight away if only one of the four plugs is at fault....

I have heared about this problem on brand new vehicles and it is often beyond the service guys to even detect it let alone cure it. My M reg Mondeo does it a bit but I just add or subtract the odd mile per hour from my speed. My WBX does it a bit (when the effing thing is not broken down) but frankly my spending hours reading up then hours fiddling days are over. The complex interaction between ancient electronics, carbon tracks, wiping contacts, vibrating solenoids and a whole load of air pipes and some might say over complicated sensors after twenty odd years is bound to be a bit eratic. I have learned to live with it.
Glum Wolfie

Can't find the old plugs to retry those..... are my new ones the right ones, Bosch WR7DC ? WIKI doesn't mention these!

Have you thought about replacing the fuel filters or even having the fuel pressure checked ?

OR just simply checking the wiring/connectors on the fuel pump....

Regards


Fritz,,,,,,,,,,,

Well, it's all down to an exact interpretation of bucking, isn't it..

Because there's 'bucking' and 'coughing', 'hesitation', 'big weak flat spots' etc

Snatching and even bucking, when coming off a neutral throttle, can also be one sympton of a rich* mixture too. Try driving a car with a manual choke left out too long, or a very blocked airfilter. It'll reach a stage when it's almost stop or go, hesitating then racing off, and perhaps 'bucking' a bit in between It's rather like a large wave of torque surging and dying, as it runs past it's ability to cope, and dies till it's discharged all the excess fuel (effectively flooding it) and the mixture gets back to normal/rich when it flies off again.

In your case it might be the AFM, air leak affecting metering, but also drippy old injectors.

It could also be a helluva lot of carbon around the valve stems and combustion chamber, soaking up the fuel on very light throttle weak mixtures, but think that would be uncommon.

It might also be exactly what some say above, air leak, weakness hesitation - you decide (is it rattly bronchitic hesitation - or the rich sort I describe above).

It doesn't sound at all like it's pinking, so presume we can rule out that timing or fuel issue, but while troibleshooting, wouldn't do any harm to run it on super. Sounds like you'd know, surely, if it was over advanced ?

Defintely Temp 2 sender or its' wiring (fractured) can do this too, and wiring to the ISU (if moving any of it alters idel rpm/idle sound then suspect it)
Hall senders usually fail altogether, but..

ThorAlex wrote:The last thing I do is to rev the hell out of that damned thing Seems like revving it to 4-5000 every time I accelerate will make it jump less at low revs. Not sure how that could help you, but it seems to keep the problem at bay on mine.

* Richness! This clears excess (unburnt) fuel and de-fouls the plugs. So id the sparks are weak or the fuel to much, it sorts it for a while...