Rough Idle???

[[email protected]]

My 2004 A4 1.8t Quattro idles rough. I cannot tell if there is a vacuum leak or what, but it bugs the hell out of me. Without going to the dealership, is there any ways for me to diagnose the problem and possibly fix it? Any ideas?

Thanks a lot everyone!

[A4_Mike]

Do you have a CEL? If so, you can go to AutoZone and they'll give you the codes (and clear them) for free.

If you do not have a CEL, check:

1. Check Valves (for a boost leak)
2. Ignition Coils
3. Spark Plugs

The issue may be something else, but I'll bet that it is either a bad check valve or an ignition coil going bad. Make sure to check the check valve immediately behind the engine.

[[email protected]]

Thanks for your reply. No CEL. I can check the spark plugs just fine, but I am not too sure about the other two.

Where are the valves I should check and how do I check them? What do I need to look for?

Where are the ignition coils and how do I check them? What do I need to look for?

Thanks a whole lot, and I apologize for all the questions?

[Stockton]

I'm in the same boat. Mine's almost unnoticeable but I notice it and I just know it's not gunna get better on it's own.

[[email protected]]

Just out of curiosity, how do you think it is just going to fix itself? LOL!

[A4_Mike]

In regards to the ignition coils, check the following DYI. Bad ignition coils give a very rough idle, loss of power, and a CEL.

In regards to check valves, check the following thread to see some examples of check valves that are worn out. The particular check valve that I was talking about in my previous post is located in the red circle (see the photograph below - credit to ActiveMonkey for the original photograph). I once had a rough idle with no CEL that was a result of the above mentioned check valve having been damaged in half. The car was fine at speed, but it was rough at idle.



If I were you, I would first check all of the check valves and then proceed to see if your ignition coils are going out. One of my ignition coils went out on me at approximately 62,000 miles, but the car became really rough (at speed and at idle) in a matter of seconds and it immediately produced a CEL. I hope this helps and keep us updated.

[kyran A4]

When I blew a coil in my engine the thing was just straight rough. Rough at all times, it went into limp mode. I couldnt go over like 3,000 rpms. We had all of them replaced and that was at like 46,000 miles. If it were a blown coil pack you wouldnt just be idling rough, as far as my knowledge goes .

[[email protected]]

Thanks yo! So I have a feeling it is not a coil pack, because it isn't that rough. Just when I am stopped. When I place it in neutral, it idles like a dream. So this makes me think drivetrain? What do you think?

I really know nothing about this as of yet, but the more I learn the better off we all are ;) Thanks a lot and sorry about all the ?????

[[email protected]]

It doesn't idle rough ever, just slight-moderate while stopped.

[02silverb6]

I am having the same problem with my car except its only when im starting my car

Anyone have any suggestions?

[HeHateMe]

When I blew a coil in my engine the thing was just straight rough. Rough at all times, it went into limp mode. I couldnt go over like 3,000 rpms. We had all of them replaced and that was at like 46,000 miles. If it were a blown coil pack you wouldnt just be idling rough, as far as my knowledge goes .

I 've had CPs go and the car would feel ok as long as I didn't go over 3500 or so. Then it would misfire like crazy. As long as I was gentle with the car, I could still drive it. I wouldn't recommend it though.

[kwan]

Without a smoke tester or vag com to check MVBs, I'd suggest wiggling check valves with the engine at idle. Check vacuum lines and hoses for tears/cracks. Tell tale signs are oil/dirt patches or hissing noises. Check for faults even though you don't have a CEL on, could be something stored. Without something solid to go by all these potential fixes are guesses.

[Stockton]

Just out of curiosity, how do you think it is just going to fix itself? LOL!

No, I didn't think it was gunna fix itself. I was saying that I don't want to just ignore it cause it's a car, it won't fix itself I'm sure it will only get worse and turn into a bigger problem if not addressed.

[drmarcj]

Depending on what you mean by "rough" idle, could be your snub mount. I had a good steady RPM (1000 at cold start, shifting quickly to a steady 800) but lots of cabin vibration. My idle got better after I reseated my snub. It's still not perfect but for instance my steering wheel doesn't shake anymore.

[[email protected]]

Okay, so the car runs great at any RPM. It idles rough when I am stopped and it is in DRIVE. When it is in neutral it feels fine. That's why it makes me think DRIVETRAIN. What do you guys think?

Do you have any suggestions on manuals I can acquire to locate all vacuum lines. Under the hood is very difficult to see things, even with all the plastic covers removed. It was easy to find all vacuum lines in my Celica, but this is a different story. If I could find all the vacuum lines, I'd be okay, but I can't.

Also, I do here a hissing underneath the passenger side, rear door. That makes me think fuel pump. What do you guys think about that too?

Thanks everyone, you are all awesome!

[jonsaudi]

I've got the same problem. I replaced the vacuum hoses, and coil packs already..still idling roughly when in gear at a stop. Haven't looked into the check valves yet and snub mount..how about you? have u checked the check valves and replaced snub mount yet? Let me know if it's made a difference. I've been having this problem since I got the car..I've looked at postings pertaining to this topic but no direct solution yet...others say they're made that way?!?!

[drmarcj]

The fact that it's worse in gear fits with my (wild-assed) snub mount theory. You could try just reseating yours for now and see if you notice any improvement at all. Check the instructions on the APR site - it's not that hard to do.

[skeeball]

I think everyone here needs to define what they mean by rough idle. Do you feel actual vibrations, or is that the RPM's are erratic or bouncing. It sounds like there are two different problems being discussed in this thread.

[demea]

I think alot of tip owners have this. Chalk me up for having the same exact issue.
2004 1.8TQ Tip / 47000 miles

[demea]

I think everyone here needs to define what they mean by rough idle. Do you feel actual vibrations, or is that the RPM's are erratic or bouncing. It sounds like there are two different problems being discussed in this thread.

In Drive = slight vibration within cabin. No hesitation in RPMs
In Neutral or park = no vibration / normal
At speed = normal

[J-jizzle]

I am having the same problem with my car except its only when im starting my car

Anyone have any suggestions?

Idk if this applies to you but I had the same problem after installing my 004 BOV. I had very ruff irratic idle on cold start ups like my BOV was open slightly. (it would sometimes die if you didnt tap the gas.) After a few sec it would go away and be fine. All I had to do to fix it though was put in a stiffer spring, all it good now.

[jonsaudi]

In Drive = slight vibration within cabin. No hesitation in RPMs
In Neutral or park = no vibration / normal
At speed = normal

Exactly.

[skeeball]

If the car is vibrating, I would check your snub mount for cracks/chunks missing. If you haven't replaced it yet, it would be a good idea to do so at this point anyway. The 1.8T installation is a piece of cake.

[A4_Mike]

On the topic of check valves...

The purpose of a check valve is to allow air flow in a single direction. They're located through out the engine bay (1.8T engine) with the most obvious one being above the air box on the left hand side. Below are poor quality, yet effective, photographs comparing a brand new (and functional) check valve to one that looks like it's deteriorating (but is still functional).





To check the functionality of a particular check valve, first remove it from the hose - this will more than likely require you to remove the clamps that are securing it. Blow into the check valve - checking both openings. Air should flow in one direction only. Using the above photos as an example, the arrow on the check valve indicates the direction in which the air should be able to flow in.

The above photos prove a good point. One can not determine the functionality of a particular check valve from simple visual inspection unless it is clearly broken in half. This was the case for me when I started having issues with a boost leak coming from the check valve directly behind the engine - the valve was broken in half between the gray and black pieces. The check valve that looks like it is deteriorating came from above the air box. From just looking at the engine bay, the check valve behind the engine looked fine until I actually went to remove it.

I hope the above helps those of you still contemplating whether a boost leak is occurring due to a nonfunctional check valve is causing an issue.

[dirtybrd]

A bad snub will only cause a clunk under accel or decel, unless its misadjusted. To me it sounds like you motor mounts are collapsed. Put of the under belly pan and look at the mounts for a reddish fluid.

[A4Shizl]

Check the hose off the diverter valve... this was the source of my rough idel...

[jonsaudi]

Check the hose off the diverter valve... this was the source of my rough idel...

Where is that exactly?? Anyone have pix??

[[email protected]]

Where is that exactly?? Anyone have pix??

Ditto!

[A4TL]

if you haven't replaced all of your braided lines; it is time.

trust me.

same goes for check valve(s). my check valve crumbled and got sucked into the $96 (160 at dealer) N80 purge valve.

talk about a pisser.

hard starts (esp after refueling)
mushy brakes

in general the 4 cylinder is pretty bad for idle with a snub mount and worn out engine mounts :)

[diagnosticator]

Okay, so the car runs great at any RPM. It idles rough when I am stopped and it is in DRIVE. When it is in neutral it feels fine. That's why it makes me think DRIVETRAIN. What do you guys think?

Do you have any suggestions on manuals I can acquire to locate all vacuum lines. Under the hood is very difficult to see things, even with all the plastic covers removed. It was easy to find all vacuum lines in my Celica, but this is a different story. If I could find all the vacuum lines, I'd be okay, but I can't.

Also, I do here a hissing underneath the passenger side, rear door. That makes me think fuel pump. What do you guys think about that too?

Thanks everyone, you are all awesome!

Yes, fuel pump. Replace the fuel filter asap. '03s has a recall on fuel pumps, check if that is needed still by your VIN, at the dealership.

The "rough" idle you describe in Drive, is a normal aspect of an Auto trans. But regardless, the vibration can be reduced or practically eliminated by careful adjustment of the front torque reaction snubber mounting. The adjustment must be performed in D, with the engine idling.
The mounting pocket bolted to the body, is loosened, and positioned so that the vibration is minimized, then bolts tightened before shifting out of D to Park/Neutral. The car needs to be on ramps, while a helper in the drivers seat holds the brakes applied during adjustment of the mount. The car must be fully warmed up before starting this task also. Minimum vibration in D can be further optimized by increasing or decreasing the idle speed a little bit, +/- 10, or 20 rpm can make a big difference. My '03, idles in D at about 830 rpm, with almost no noticeable vibration. When shifted to Neutral, there is no vibration at all, the only way to know that the engine is running (with the radio volume turned up,)is to look at the tach.

Acceptable results depends on the condition of the main engine and trans mounts as mentioned already. The main mounts must be OK for sure.

[[email protected]]

Awesome, thanks a lot! I will reset my snub mount later this weekend and let you know how it goes. I can't thank you all enough!

[Albo74]

Hey 04b6sport, did you get a resolution on this issue. I am experiencing the same thing.

Many thanks.

[Albo74]

Finally got the issue resolved. It was a dirty intake valve that needed a little cleaning.