Jerking below 2k RPM
 

Hi!

I get some jerking below 2k RPM on my S5 TII engine (this is engine relevant, right? :P )

The jerking is accompanied by my tach going up and down in the same rhythm, maybe every 3/4 second or so. It was gone some time, but came back. The things I can think of is ignition timing, non-working BAC, vac leak or TPS out of range.

However, the timing is good, some degrees off, that is, where it runs as smooth as it can. BAC is not connected at all, there are no vac leaks, and the TPSes was adjusted straight before summer.

Your TPS is out of adjustment.

Sure you may have adjusted it, but it could be just bad. Mine is 100% completely within spec in adjustment and it still does the same thing. Why? Bc I sprayed it with brake clean like an idiot without thinking about it. But before I did that, it was out of adjustment and did that same thing, then I adjusted it and everything was good. Sprayed with brake clean, now I'm back at that problem.

Btw, what do you possibly think you gain from having no BAC? Put it back on, that is also contributing to your problem.

No it is not. It wasn't like this before. This BAC I got recently. However, it is from a N/A S4, so the air nipple is on the wrong side, so I have to MacGyver the hose.

As for the TPS, it might be. But I never used brake clean for it. I used start gas when checking for vac leaks AFTER it became like this. So no reason for it to suddenly do that.

Also, it came, then went, somethings I did touch, something I did not touch, the TPS I did not.

there is no use in removing the BAC pretty pointess if you ask me

Much like your post :scratch:

But you just never know on cars our age. Things can just randomly let go for no apparent reason. The TPS was just fine when I bought the car and randomly went out. Replaced it, adjusted it, ran perfect. Got the freaking brake clean on it while cleaning the TB, and poof, went to shit again. So having dealt with it a couple times, I'm going to say that is MOST LIKELY your problem. May be worth just checking other things (maybe something is loosely connected, maybe a different sensor is bad, maybe this maybe that...), but I'm standing my ground with the TPS.

Edit: when was the last time you cleaned your grounds? I would do that also and apply dielectric grease to the surfaces and bolt threads when you put them back on.

The grounds were cleaned around May-June sometime. Wire brush, electronic cleaner spray can for the fun of it, and dielectric grease on the bolts, just as I am supposed to.

The jerking seems to come whenever there is a hot chick in a radius of 20 meters, horny little bastard this car is!

On the more serious note, if I find my BAC block-off plate again, I can put that on instead of having it there without having it plugged in, it is a spring based thing that vibrates, I guess it could leak, in theory?

If it is affecting your tachometer, it may be a timing issue.

Have you recently messed with the CAS?

Well, if the car is jerking, the engine is as long as it in gear. And if the engine is jerking the tach will move accordingly.

But I did adjust the timing a bit now, much less jerking. I turned it so the rear part of the CAS is closest to the bolt, in other words it is turned more to the front. Now, is this retarding or advancing it?

If I am reading that correctly, that would be advancing.

sounds like the tps. I had the same problem, I replaced the tps

I had a totally different problem when my TPS connector was bad. Swapped it for 6 separate connectors, no problem.

If this is the TPS, it is an adjustment problem, nothing more.

Six separate connectors? You mean you tried six different throttle positioning sensors?

Did you use a lighting light when you played with the CAS? You cant just go tinkering with things just so it "feels better" And yes Pnoyrx7 is right with his so called useless post. No point what so ever in removing the BAC....it is there for a reason ya know.

+1!

No, I mean it started acting, it was the CONNECTOR, I swapped the single 6-pin for 6 1-pins (in lack of a six-pin), and it worked again.

Now it is acting up in a totally different manner. No brake cleaner near it, no nothing on the TPS.

As for CAS, lighting light? Timing light maybe, and yes. The center of the CAS is on the spot, and from there you can adjust what, 2 degrees advance/retard?

Unplug the TPS and check it according to the FSM. If it tests good, it is probably the ground n the rear rotor housing under the UIM. I know you said you already did grounds, but triple check that one.

I had a similar issue with cutting out and the tach would drop out when it would happen. The car would run fine, then cut out for a sec, then run fine. The vibrations of the engine and how loose the bolt is can cause it to happen at different revs.
If you're tricky and have the right tools, you might not need to remove the UIM to get to it.

Your tps has 6 wires?

The only reason I called it useless is because I literally just said that. I gave a little speal about it, soooooo

S5 has two TPS, so the plug is 6 pin no?

jimmydanny sig says using a S5 motor in S4 chassis. Are you using a S5 throttle body and two TPS sensors? I don't think that plugs in to S4 harness.

I know that happens, this is totally different. When that ground was weak/non-existent, the car first started like you described, then just didn't start. This is something else, this is jerking, only below 1500-2000rpm, like if you have a bad rear camber link, this is the time you will hear it. Ca-clunka-clunka-clunk would be the sound coming from my camber link. Think that covers how it jerks. The jerking is over a span of 400rpm, meaning it doesn't change more than that, and it is pretty consistent, every 0,5-0,7 second it is a new jerk-pulse, accompanied by the clunking from the rear

:P
S5 engine, S5 engine harness, S4 front harness, and the rest S4 as well.

Adjust your TPS and check your front diff mount.

TPS was adjusted, so unless it magically unadjusted itself in one day (ie not over time), it isn't the TPS.

The diff mount? the clunking you are referring to? That is the camber link, nothing else. Convertibles are too heavy in the rear to use the stock ones, already swapped out one two years ago, no the other is dead. And yes, I do recognize that exact clunking!

When was the TPS adjusted? In this thread, you're swaying you swapped in some other TPS and modified the plug. Has it been re-adjusted and tested since you started this thread?

What you're describing sounds like a bad TPS sensor. If you swapped bad for used, your "new" used one may have just taken a hike as well.

CHECK IT

So the clunking is like a rear camber link, or is a rear camber link? You're confusing me.

Double check te items I listed man. Just to rule them out, last time they were checked was when the car was running right.