Audi b7 A4 possible engine problem?

[quattro_fanatic]

Hi guys,

I"m a newbie here, I've been using these forums to help with the previous issue on my car and they have helped a lot. Unfortunately, a new issue has come up and I'm just about out of ideas on what it could be causing this. Little run down, my current daily driver is an a4 b7 Quattro s-line manual, it has the 2.0 engine in it. Randomly throughout the past couple of weeks, I'll be driving normally(not aggressive) and out of nowhere it feels like I slammed on my breaks for a split second. The rpm needle will usually dip down anywhere for 1k-2k, and then go back to normal. This has happened while accelerating and cruising on the highway. A few times this has happened when leaving a red light and unfortunately the car stalls out. I've cleaned out the TB and MAF sensor and the cam follower, timing belt, head gasket, water pump and spark plugs have all been replaced, within the last 15k. No codes have been thrown yet. This is my daily driver and I'm afraid that something else might break due to how violent this can be sometimes when it occurs, any help would be much appreciated.

[Dondbg]

So if you scan the car, you get not faults ?
Coils or fuel supply issue filter / pump ?

[quattro_fanatic]

So if you scan the car, you get not faults ?
Coils or fuel supply issue filter / pump ?

Yup zero faults, I was thinking maybe coils but could a misfire really throw the car like that?


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[Theiceman]

and a misfire would set a code for sure .
is it like instantly taking your foot off the gas or something more ? without coeds this could be tough , anything from lpfp giving out to complete engine cut.

[Deathgrip]

I've seen PCMs do weird things like that.
They won't throw a code on themselves either.

[quattro_fanatic]

and a misfire would set a code for sure .
is it like instantly taking your foot off the gas or something more ? without coeds this could be tough , anything from lpfp giving out to complete engine cut.

No it’s more, the car doesn’t coast for a second or two. Honestly the best way I can describe it is, say your going about 75 and than u slam the brakes for a split second. When this engine cut out happens that’s the closest thing to what it feels like. I was reading a post on a different website a little similar to this, he was that he believed it could me the camshaft position sensor, but I feel like it may be more a computer related issue


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[quattro_fanatic]

I've seen PCMs do weird things like that.
They won't throw a code on themselves either.

Really, that’s weird, anyway known how to possibly test that?


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[Deathgrip]

Really, that’s weird, anyway known how to possibly test that?

I've just swapped them with junkyard pulls.

[swalkerman]

This sounds a lot like a problem I had with my A4 - perhaps this will help: when this first happened to me, I was pulling away from a stop sign, and the car bucked and stumbled violently - much worse than hitting the rev limiter (which I was nowhere near anyway). The rpm needle bounced around while this was happening. In my case, it only happened with moderate acceleration; if I drove like a granny, the car behaved normally. I provoked it into this condition several times to see what would cause it, and eventually the check engine light came on. The code was something like "crank position sensor signal implausible". After a couple of start-stop cycles and gentle driving, the check engine light went off on its own.

I took the car to a local independent Audi mechanic, and described the problem to him. The only thing he suggested was replacing the N205 valve (variable valve timing control solenoid). So, I bought a crank position sensor and an N205, but I only replaced the N205. Since then, I think the problem is solved - it has not come back since, and I have driven the car vigorously enough to repeat the conditions under which it happened originally. I also think the engine is running better (smoother) than ever. (I'm not the original owner - the car now has about 120K miles on it, and I bought it with 102k). The N205 is pricey, but very easy to change.

[Theiceman]

well lets think about his for a second .. if he was not getting ignition he would dead head the cylinder. under compression as there is no spark and it would act like its braking the car. no ?

so the thoughts on the comouter would make sense. of course the crank and cam need to be seen to make spark too.

[B7S3wannabi]

I'm betting on the throttle body or connection to it.
Might try tugging on the pigtail in all directions to see if it makes any difference. Might consider crimping the terminals while you're at it to tighten them up.
Sounds like the throttle plate closing spontaneously.


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[BillyK]

Does this happen when the car is still warming up? This happens with my car at between 8-10 minutes after starting a trip and not again after. It happens almost every trip if the car sits long enough. I still have not found a solution.


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[quattro_fanatic]

Does this happen when the car is still warming up? This happens with my car at between 8-10 minutes after starting a trip and not again after. It happens almost every trip if the car sits long enough. I still have not found a solution.


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I’ve actually noticed that it happens when the engine is warm, when it’s cold in the morning I don’t think it’s ever happened


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[quattro_fanatic]

I'm betting on the throttle body or connection to it.
Might try tugging on the pigtail in all directions to see if it makes any difference. Might consider crimping the terminals while you're at it to tighten them up.
Sounds like the throttle plate closing spontaneously.


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Would the butterfly closing on the TB cause such a violent jerk of the car?


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[B7S3wannabi]

Hard to say since I have not experienced the severity of your symptoms.

If it is THAT violent I would move more towards internal of the engine, trans, axles, driveshaft, or differential.
Essentially any rotating assembly.
First inspect axle joints and driveshaft u-joints for movement or binding.
Try power braking with the parking brake up and slipping the clutch to put as much stress on the drivetrain components as possible while not stalling or breaking loose.
Make note of EVERY driving condition when this happens. Is it raining? Outside temperature? Speed? Condition of the road? Turning? Straight? Etc.


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[quattro_fanatic]

Hard to say since I have not experienced the severity of your symptoms.

If it is THAT violent I would move more towards internal of the engine, trans, axles, driveshaft, or differential.
Essentially any rotating assembly.
First inspect axle joints and driveshaft u-joints for movement or binding.
Try power braking with the parking brake up and slipping the clutch to put as much stress on the drivetrain components as possible while not stalling or breaking loose.
Make note of EVERY driving condition when this happens. Is it raining? Outside temperature? Speed? Condition of the road? Turning? Straight? Etc.


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What would putting that much stress on the drivetrain do exactly? But as for the conditions, it has happened in all 6 gears but most frequently in 1st & 2nd, it has happened at all speeds. Whether it be leaving from a red light or going 80 down the freeway. It’s honestly very random, I’ve tried to recreate the issue several times but have had no luck. I don’t know if this helps, but the first time it ever happened was when I was driving back from mammoth. That’s a decent journey close to 700 miles for me, I thought it had to do with the cheap fuel I put into it along the way because when I got back home I put some premium in it & the issue went away for a good month I’d say, but than it returned.


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[wt8d]

Sounds like engine speed sensor(crank position sensor) problem. Sometimes it does not throw any codes.

[ahotboy15]

ive never even looked at my spark plugs im scared to touch them but i would have tried to find a misfire and change the coil pak while i was driving. I would say due to the randomness you might get away without playing parts darts if you drive long distance maybe that is what finally burnt out something. a handy AAA might be a good deal for you just in case. your thoughts?

What would putting that much stress on the drivetrain do exactly? But as for the conditions, it has happened in all 6 gears but most frequently in 1st & 2nd, it has happened at all speeds. Whether it be leaving from a red light or going 80 down the freeway. It’s honestly very random, I’ve tried to recreate the issue several times but have had no luck. I don’t know if this helps, but the first time it ever happened was when I was driving back from mammoth. That’s a decent journey close to 700 miles for me, I thought it had to do with the cheap fuel I put into it along the way because when I got back home I put some premium in it & the issue went away for a good month I’d say, but than it returned.


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[ahotboy15]

some of those tests sound too violent that he might lose power to his car. If thats the case wouldnt you inspect more of the computers than the internals?

Hard to say since I have not experienced the severity of your symptoms.

If it is THAT violent I would move more towards internal of the engine, trans, axles, driveshaft, or differential.
Essentially any rotating assembly.
First inspect axle joints and driveshaft u-joints for movement or binding.
Try power braking with the parking brake up and slipping the clutch to put as much stress on the drivetrain components as possible while not stalling or breaking loose.
Make note of EVERY driving condition when this happens. Is it raining? Outside temperature? Speed? Condition of the road? Turning? Straight? Etc.


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[B7S3wannabi]

some of those tests sound too violent that he might lose power to his car. If thats the case wouldnt you inspect more of the computers than the internals?

I don't even know how to respond to you without losing my shit...



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[B7S3wannabi]

What would putting that much stress on the drivetrain do exactly? But as for the conditions, it has happened in all 6 gears but most frequently in 1st & 2nd, it has happened at all speeds. Whether it be leaving from a red light or going 80 down the freeway. It’s honestly very random, I’ve tried to recreate the issue several times but have had no luck. I don’t know if this helps, but the first time it ever happened was when I was driving back from mammoth. That’s a decent journey close to 700 miles for me, I thought it had to do with the cheap fuel I put into it along the way because when I got back home I put some premium in it & the issue went away for a good month I’d say, but than it returned.


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You only need to do it in short bursts. If you do this too long you risk smoking your clutch.
This test is used for testing engine mounts and possible issues with bad axle joints, u-joints, ring and pinion gears, etc. it puts a load on everything and if something is loose or failing, this test helps find the issue. It could cause the joint or gear to essentially slip and make the symptoms you may be experiencing.
It's only a test. It may show you nothing. Or it may point you in some kind of direction.


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[supple]

So I've had similar issues although not quite as "violent" as you've experienced. B7S3wannabi has a point. The symptoms are pointing to either the throttle body, its connectors, or possibly the crank position sensor.
Personally I replaced the connector and wires on the throttle body, there's a DIY for it and pretty easy to do. You can check this when the engine is running, just push/wiggle the wires around close to the throttle body connector to see if it makes it idle rough/