Weird Thud While Idling... Cause?

[sl33py]

Hi.

Just bought a Series 2 R33. The engine is stock, with just an aftermarket exhaust and a K&N panel filter in the box.

While I'm idling at the lights, every say... 10-15 seconds or so... I'll feel something like someone hitting the back of the car with a basball bat. I reckon it's in the exhaust system cos I hear what feels like the engine nearly misfiring... it's weird. But I don't think its an actual misfire cos that would be every cycle right? and this is only every 10-15 seconds.

First time I noticed it, I had the A/C on. I'm used to a civic where if i had the A/C on u REALLY new about it.. car lost all guts and u could feel the A/C cut in and out while idling.. I thought this might be the same. I think it *may* have lessened the severity but that may just be wishful thinking. I don't think it should be doing it at all, eh...

Car is under warranty and I can get it fixed for free if needed, but I'm just wondering if this really is something "wrong" and wanna know what it is before bothering to go back for something that may not need repairing (I'd be surprised if it doesn't though.. it's a bit freaky when ur sitting there and suddenly it feels like someone gives u a right royal kick in the pants lol). Even my gf looked at me the first time and went "wtf was that?!" and she has NFI about cars.

Didn't notice during the test drive cos was having too much fun.. and the NRMA report didn't turn up anything untoward.

Anyway, interested in suggestions. Thanks in advance.

[R33S2]

You mentioned the aircon, does it do it when its off? Is it an auto? Is it backfiring?

[DriftSquad]

coil packs? or maybe it needs some 98% octan fuel

[sl33py]

I've been running 98 fuel only. Well I said it was maybe worse with the AC on compared to off in my post, so yes it still does it with AC off.

I described it to a friend who drove it and he said it's just the engine running rich to help cool down the turbo once it's done some work. He also said it shouldn't do it at all when the engine has just started up, but that it's expected if the engine/turbo have warmed up a bit after spirited driving.

IF this IS the case, I'd be surprised if the 'thud' is meant to kick as hard as it does. Gonna investigate and test more of when it does/doesn't do it. Doesn't sound like anyone else's does this though, which isn't too encouraging.

[sl33py]

OK after further investigation:

A) It doesn't do it at all if I start her up cold in the morning and just let her sit there idling.

B) When I was at the lights after 10-12 minutes casual driving (mostly 80km/h between town centres and then about 5 minutes of 60km/h.. so pertty easy going, barely boosted). I listened and heard/felt: car idling and there isn't actually any popping at all. I know what back firing sounds like. This literally feels and sounds like a miss... engines running fine and every say... 5-10 seconds it sounds like the engine simply misses a beat. Sucks. gonna take it to my mate and point it out to him, see what he thinks cos he only drove the car before i noticed and mentioned this sound, he might be able to tell me more if i knows what i'm talking about first hand. A missing cylinder isn't actually audible as a "miss" in the sound of the engine running, right? cos it misses thousands of times a second doesn't it?

So I'm at a bit of a loss to what this might be. I might rock up to the local gathering (ACT national museum) and have a few other 'line owner listen and tell me if I should worry or if I'm just paranoid.

[Links]

Hmm.. sounds a bit strange, sometimes when idling mine will get a little rough.. but can even this out by just touching the throttle a little bit..

The RPM's should go up a little bit when the Aircon is turned on as the ECU should automatically adjust the idle RPM according to the power required.

You could try resetting the ECU and get it to re-learn it's timing as per the new fuel and so on and so forth..

I don't know about the whole "it's running rich to cool it down" even after pushing mine very hard it's still idling pretty well - maybe if you turn it off than back on it has trouble hunting for a idle RPM.

Get a couple of other guys to listen to it and see what they think - it's a bit hard to guess at what it is when we can't hear it..

Does the car have HICAS? what year model is it? When was it brought into Australia?

[Links]

You forgot to mention whether you have an aftermarket BOV or not - if you do these are known to cause issues with idling/stalling in skylines.

[sl33py]

First post: Engine is stock cept the exhaust.

Yeah, I notice the more obvious engine activity while A/C cut in and out while idling.

Yep, gonna have a few locals listen to it, see what they think.

It's a 10/96 R33 GTS-T coupe with HICAS. Came into the country 05/04. In fact, looks exactly like ur car Links. Go the silver

[hbs2jh]

i fink it's coil pack or spark plug or leak from exhaust or from air filter..

clean ur air filter dat's one thing u can do.. other stuff u hab to get check up at mechanics.. good luck with fixing it.

coz i had three prob with my car.. coils and plug and filter..

i hab to fixed all except to chane coils..

waiting for coils to come..

[driftmeister]

My car seem to hav the same problem (with a/c on is more prominent), but mine is a R34 GTT manual, 3" exhaust, air filter and new HKS plugs (range 7) because it happened with the old NGK plugs too. The funny thing is everything ran fine when the new plugs when in for a month then just last week I change the timing belt ("Power" Jap brand), the miss came back again. It usually gets more frequent misses intervals during the afternoon.

Anything to do with timing or coils? Not sure whether I need to reset the computer again? Appreciate advice

Newbie

[driftmeister]

My car seem to hav the same problem (with a/c on is more prominent), but mine is a R34 GTT manual, 3" exhaust, air filter and new HKS plugs (range 7) because it happened with the old NGK plugs too. The funny thing is everything ran fine when the new plugs when in for a month then just last week I change the timing belt ("Power" Jap brand), the miss came back again. It usually gets more frequent misses intervals during the afternoon.

Anything to do with timing or coils? Not sure whether I need to reset the computer again? Appreciate advice

Newbie

[turbohectics]

My friend said its running lean on idle,

My line does it to every 15 seconds like a small hickup.

Wouldn't mind knowing whats going on

He might be right ,anyone got a solution ?

[Daniel_]

Noticed mine doing it at idle today too (r34 GTT auto) wouldn't say a baseball bat bit a little nudge for sure.

[CWest]

Guys Ive had my R34 for about 3 years now. Anytime I have issues with misfiring etc I look at the coil packs. It never happens when its cold only after 10 mins or so and the check engine light comes on.

I now just check the coil packs, have had to replace 3 in the last 3 years. Either Araldite them or just buy 2nd hand ones. It seems to be a reasonably commom issue, for me anyhow.

[turbohectics]

i got brand new splitfires Di !!! Must be something else i did notice my canon is leaking exhaust gas ses ,anywayz back to standard or quiter as I'm off to the EPA very soon waiting for letter in the mail !

[sl33py]

OK So we checked out the coilpacks: they look fine. They are the original stock ones, but there are no signs whatsoever of the arcing, e.g. strange burn marks or whatever on the sides of the packs, or scorch marks on the internal of the engine.

So then we pulled off the O2 sensor and found that the car runs exactly the same with it connected and disconnected!! The reading on the sensor was a permanent ZILCH. My mate said that most jap O2 sensors operate between 0.4 and 0.6 volts, and that 0.5V is the reading that it is ultimately trying to maintain. He reckons the car is running real rich and may be in what he called "limp home" mode .. or something like that. We're gonna swap out the sensor for a new one and see what happens. From the sounds of things its a good thing to fix/replace anyway, even if it's not the solution for my misfiring. I'll post my findings.

[sl33py]

Oh and we also checked the sparkplugs. The dealer did replace them as stated.

[sl33py]

O2 sensor didn't change anything with respect to the misfire at idle, but the car seems a bit more responsive now. The new sensor gave the measurements expected when it was hooked up. During the first 3 minutes of idling after hookup, there was no misfire, but then after a quick hoon, it presented itself again *sigh*

[sl33py]

FOUND! Had it into the mechanics today. He said that when he adjusted the throttle position sensor, it idled 15 minutes without a single miss (and sounded much better too), but as soon as he went for a drive in it, it started again.

If I understood what he told me correctly: He attached an oscilliscope to it (and a lot of other things too) and said when he gave the throttle position sensor a tap it sent the signal absolutely spac and it misfired like crazy and then when he left it, it misifred at the intervals I've been seeing. So I'm ordering one tomorrw (he recommended JustJap, any other suggestions where I should check?) and he said he'd install it for free since he's got all his money for just diagnosing it. I've looked on eBay and even a Porsche TPS is only 40AU, which makes me hopeful that I'll get away with a secondhand one for maybe 30-50 at worst. I'll post again when it's replaced and I'm 100% it's solved. So everyone check ur TPS!

[sigsputnik]

jeez it hasn't been an easy intro to skylines for you, has it!