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Vedad1944

Engine revs itself to redline

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Vedad1944

Hello everyone!

I've had quite the adventure in the past two years driving this car. It's quite the old car, but I kind of like the character these have. Problems pop up, and go away over time, most of them ignorable, but this one was a nasty surprise.

I drive 1995 Ibiza 6K with a 1.4 8v ABD. I know, I know, it's not a Polo 6N but they're very similar so I was hoping if someone would help me here. All of the other SEAT-related forums seem to be just related to the newest cars or just downright dead. No help whatsoever. :/

I once again apologize for it not being a Polo, I just can't find anyone with this specific problem.

 

What happened prior to the problem:

Spoiler

 

So it went like this, during rainy days it would stall, ignoring my throttle input completely, the car stuttering and whatnot. (After a whole heap of trial and error) I saw that the plastic under the wipers and pressed on the windshield isn't fixed or glued to it by any means, so (thinking that water might be making a short circuit somewhere and removing ignition) I used some silicone make a proper seal. This stuff worked magic, it stopped the stalling completely and the problem was gone.

 

My dizzy went 2 weeks after that, and replaced it with a used one. Idle rpm odlly went up from 600 to 750, the mechanic saying that 750 is what it's supposed to be, and 600 is too low for petrol cars.

Two months after that, my battery light would never light up again as I turn the ignition on. We tried disconnecting the clip from the alternator (the single green wire to test it), and it still didn't light up. I checked the light-bulb itself and it wasn't blown. I ignore it, but I noticed that when I start my car in the morning it would start stalling after 2 minutes if it didn't blip the throttle to 2000RPM.

The dash would light up brighter and the headlights would go stronger quite noticeably. I ignore it, and just teach myself to rev the engine every time it start the car.

 

 

The other day, the weather is damp, and the car started oscillating it's revs in a rhythmic way between 750 and 1200 rpm (idle and warm up revs), it is about to stall, but then it gives itself some throttle and goes to 1200 but then stalls to about 750 and throttles itself again until I intervene with a quick blip of the throttle and it goes away. It was odd, and enough to get my attention. After about a month, I decided to reset my ECU, so I disconnect the battery overnight and after 24 hrs I reconnect it and start the car. I let it run and it got down to 750.

 

10 minutes later, down the road, I stop my car at a stoplight, and it starts oscillating again, I blip the throttle, and it just revs itself to redline! It does not take any throttle input anymore, and I just cut the ignition. I start it up again, and it revs itself again to redline. I was afraid to dump the clutch to see if it would keep going, but I pushed the car to the side of the road and tried to see what was going on.

The mechanic replaces the throttle actuator, and it went away for 15 minutes. Second replacement, 600RPM and it was away for 10 minutes, then the 3rd one was okay for 3 weeks.

 

Now, I was having some short-lived fun, where I used full throttle, the car pulled no problem from 2000rpm to 5000rpm. And 2 minutes after that, at a carpark it's idle went from 750 to 1000, and when I tried parking, it again went to redline, same problem, whatever I try (it was wet outside again). When I turn the ignition on, the butterfly valve is wide open, is it supposed to be like that?

I've searched high and low for answers, from one forum to the next, 2003 to 2015, I've learned how Monomotronic/Jetronic is supposed to work, what inputs it takes in, how it operates and whatnot. My mechanic has a parts car, so I can get replacements right away, I just don't want to burn a hole in my pocket (it's charred as it is :/)

The car sits for 3-5 hrs and the problem goes away, but I'm afraid to make any longer journey in it.

 

Can the actuator even push the throttle body all the way to wide-open? Could the ECU be knackered? I understand that all it takes is a small short circuit between the contacts on the ECU and the actuator goes out all the way, but W.O.T.? No way. I'm lucky it's not an automatic.

 

If anyone can help me narrow down the possible problems, I would be very grateful!

I have heaps more info I got from observation research of the car, but no-one had a W.O.T. problem like I do.

 

P.S. The MPG was usually 26, but during winter it drops to 14. Any help with that would be good as well!

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kiran_182

Have you checked the trottle cable moves smoothly in the outer sleeve?

 

Is there a throttle position sensor?

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Vedad1944

Well, according to the Monomotronic manual it states that there is a potentiometer directly connected to the butterfly valve. That might be acting like a throttle position sensor. I haven't had any problems with the cable sticking, I just blip the gas during the rhythmic revving (just a quick light touch), and the engine goes haywire.

I started the engine just now, it's -11C outside, and it goes to 600RPM, waited for 15 secs, I rev it to get the alternator going, it goes back to 600, then keeps rising the revs to 2000, and drops it to 1200 for warm up.

After that it ran fine.

Could be the potentiometer, I might try just replacing it. The manual says that there is no serviceable parts inside, hah like I care.

 

Could the ECU be the culprit for the battery light?

 

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kiran_182

The cold may be a factor, once warm if the car is ok and its always ok when warm you may just have to plan 10 - 20 min warm up into your routeen

 

 

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dvderlm

vacuum leak ?

like at brake servo tube

(falschluft) 

All the pressure and temperature lookup tables in Ecu will be nearly out of range, but loads of air is reaching engine, so Ecu thinks you've got wide open throttle and injects more fuel...

it redlines. 

 

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Vedad1944

Where can I start looking for a vacuum leak? I know a very thin hose going from the "control box" on the intake, and then there's one behind the injector unit next to the firewall?

Is the canister under the right headlight a vacuum canister?

My car came with vacuum operated central locking, but that is long broken, could it pull air from one of those and then screw up the signal somehow?

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Vedad1944

Is this supposed to be connected to something? I'm thinking it should mirror the hose next to it, but there is no hose that same size in the engine bay.

Picture is taken from the firewall.

You can see the throttle cable return spring on the right.

pic1.png

Edited by Vedad1944

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dvderlm

Sorry don't have such a car to compare. Put a tube on it and hold tongue to a finger or cheek or tongue. If it sucks when you run engine there's a leak there.

 

Cut tube shorter, block with a bolt and jubilee clip.

 

Hard plastic tube to brake servo can be a leak spot.

Shaving foam will bubble. Or cold start spray (diethyl ether) can indicate where a leak is, as sucked into engine changes note but no good at max revs

 

 

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Vedad1944

Thank you dvderlm, I will try this tomorrow morning!

I found a copy of Haynes Service and Repair manual for the 6N, I will try and find something relevant there as well!

I'm trying to find out what does that connection there do, closest I can find ATM is this: https://seat.7zap.com/en/e/ibiza+st/ib/1995-138/1/129-129010/

Specifically part number 7. I see it is connected to part number 11, what do they measure, temperature of the air intake?

 

This is my first car, I made my first "baby steps" in this car, and now, 2 years later I've decided to wrap my head around how it all works under the bonnet.

Egh, another day tomorrow.

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dvderlm

part number 7 is a thermo valve for controlling the warm air flap. When air filter cold flap lets warmed air from exhaust manifold in.

When air filter is warm enough valve opens, engine vacuum pulls the flap closed, so only cold air enters engine.

 

It is leaks after throttle flap that cause unwanted  revving.

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Vedad1944

Alright, so, my dad couldn't get the engine to fire up and run this morning without holding the throttle at 1500RPM for about a minute. The car ran fine after that.

I went out after the car sat for an hour and a half, temperature is -10C.

I take the airbox off, and see that there is a vacuum hose going from the thermo valve to the warm air flap and it was disconnected in the rear somewhere. I take the hose off, and clean it with some wire, it was full of black stuff (don't know if old oil or exhaust charcoal). Also, the rubber ends are all crumpled, so i put them on backwards to get them to use the fresher part.

The car starts fine, and acts completely differently, the throttle is still soft as usual, but it drops revs very quickly to idle (compared to doing it slowly). Idle varied from 750 to 850, and my brakes became super hard and sensitive (related to vacuum?).

 

But I also found another thing loose, some sort of 4 pin connector, and it was going to a canister under the right headlight. From that canister it goes to the other (vacuum?) line next to the one I just mended. Another thicker wire goes up and underneath the windshield wipers (possibly to the ECU?).

The exhaust is the closest thing to the connector (where it was hanging), and I know somebody did a crap job welding up the exhaust, judging by the bad welds and the missing cat. I don't see a lambda probe anywhere, so could this be the missing part?

Haynes says that this is some sort of charcoal canister, related to emissions, should it be cleaned every now and then?

 

Thank you in advance!

pic3.jpg

pic2.jpg

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dvderlm

Yep, the canister absorbs petrol fumes from tank, and they are purged into running engine (by vacuum) when engine is hot enough.

On old cars the tank fumes were vented to atmosphere, so the north pole is now above freezing. 

 

If it is injection engine (not carburettor) there should be a lambda probe, or it will run open loop warm-up phase or breakdown get-me-home mode. 

So will run but badly.

.

 

 

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Vedad1944

Yes, it is throttle body injection, but I've always had horrible MPG, like less than 20 during winter.

Okay, so I either have to find a catalytic converter or just the lambda probe with a bung so that I can weld it in and connect it.

I think it's both warmup and get me home mode, because each time I start up it re-does warmup, and my MPG is horrible. 

I will be doing a timing belt change in a week or two, so I might aswell try getting a lambda probe attached.

 

I'm keeping my fingers crossed that there wont be any redline fun anytime soon.

 

I will update if something pops up in between.

 

Thank you again! :)

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Vedad1944

And it didn't take me long to run back...

So just now, I was accelerating from a dead stop, I got to 2nd gear then *pop* engine jerks a little and dies. No reaction to throttle input, just a slight bump and it died in gear. I stop the car, and it starts like nothing happened. Could this be a detonation/misfire? (I have no idea how bad it is for the engine)

Could it be anything ignition related? The coil pack?

I got 18MPG out of my last tank of fuel, what could make it so bonkers bad on fuel?

I am going to the mechanic tomorrow to get it scanned with VAGCOM, could I learn anything useful from the ancient ECU?

I am going to do a whole bunch of work on the car, so I might aswell get it over with :/

 

Thank you in advance!

 

Edit: The weather was warm and dry, plus, the distributor went bad a while ago, and the way the engine bumped while in gear is similar to what happened today, except now it started right up.

 

Edited by Vedad1944

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dvderlm

I reckon ECU is giving up in limp mode because the sensor values are "off the chart" with no lambda to give closed-loop feedback.

 

How soot carbon black are the spark plugs or the exhaust pipe?

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Vedad1944

The spark plugs were changed about a month ago with Bosch ones, and the old spark plugs were basically crystal clear, no black soot or whitening.

My exhaust however has black soot present, and on a bit colder day it's really smokey compared to other petrol cars (not head gasket level smokey, I've seen that)

The exhaust does not smell very strong, just, like, a weaker petrol smell. Also there is a lot of condensation every morning coming from the exhaust, it goes away after about 3 minutes of idling.

Will get it scanned with VAGCOM, get TB alignment done, try a different potentiometer, if it does not return any codes I might get the ECU swapped to see if it makes a difference. 

Could the missing lambda probe cause 18MPG?

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dvderlm

If there are no fuel leaks (tank cap, filler pipe or tank or fuel lines or  pump or filter) then it can only be engine issue using 2x to 2.5x too much petrol.

Car would smell very badly of petrol if there is a leak.

 

But 18mpg and not soot  and not white plugs is a little  mystery. Is ignition timing right, too retarded loses power per stroke.

Do a compression test or leakdown test to check piston rings are sealing well?

 

 

 

 

 

 

 

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Yeti

Was it alright before you changed the plugs? Thinking you might have been given the wrong ones.

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Vedad1944

The situation hasn't changed after new spark plugs, I had them replaced as regular service. 

But hey, I was at the mechanic today, I found 4 trouble codes.

We cleared the codes, 1 related to the hall sensor (no signal), 1 to the lambda probe (no signal), idle switch (periodical), and throttle position sensor/potentiometer (periodical).

We cleared the codes twice, and the hall sensor code is stays on. The potentiometer code reappears after about 1 minute. 

Now, the cutout happened again just now, except it was in gear long enough that I regained power and got home okay.

Can I replace the hall sensor? It was a circular thing that I found here https://seat.7zap.com/en/e/ibiza+st/ib/1995-138/9/905-905040/#21

number 21 to be exact.

Would it pay off to replace the whole distributor? If so, can I use a distributor from a MK2 Golf 1.3? I am guessing it comes with a new hall sensor as I see a connector. https://www.olx.ba/r/21045512/241055

But now I am at a dilemma, if the hall sensor is faulty, how does my RPM gauge work?

 

Thank you to all the good people on ClubPolo!

Edited by Vedad1944

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Vedad1944

Would a Bluetooth ELM327 reader work with this car? I could get one for about 20 euros and I could hook it up to my phone. I'd be able to keep an eye on the engine with the ELM327, anyone ever used one of these before?

I've been looking on the internet, it turns out that I've developed an intermittent no spark problem. That would make sense and replacing the whole distributor would solve it I guess. Can I replace the distributor myself, preserving the timing setting somehow?

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nige8021

No they will only work on EOBDll cars post 2001 for petrol or 2004 for diesel you will need a VAG based reader that will give you the 4or5 digit fault codes VCDS that runs on a laptop is the best option 

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Vedad1944

Aww shoot, my mechanic used some sort of program called Delphi, I saw it wasn't VAGCOM but it worked anyway.

Damn, guess I will have to get a proper reader, or just go to the mechanic periodically.

I will try and find a brand new distributor with the hall sensor tomorrow and get it installed to see if it fixes the code.

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nige8021

There are other code readers that will work, like snap-on, Sykes Picavant ACR 4 but you then need the VAG specific plugin modules to get the codes

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Vedad1944

Would this cable work with VCDS? I saw a VCDS Android app aswell, have you tried using it Nige?

Screenshot_2018-03-11-21-08-21.png

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nige8021

That cable is intended for the old version of vcds, vagcom 409.1 it will give you the fault codes and allow some adjustments like the throttle body alignment, not used any android versions just the VCDS on my WinXP laptop

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