2008 Acura RDX - Idle Issues

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5 months 2 weeks ago #201277 by TKB
2008 Acura RDX - Idle Issues was created by TKB
2008 Acura RDX - 96K Miles - owned since new and I'm not a particularly heavy footed driver. Stock K23A1 engine - no mods. It has lived in a hot desert climate for most of its life without much snow or rain.

Problem description: Never had a CEL. The idle "problem" started probably 20,000 miles ago. As I recall it, the engine suddenly started idling rough after I got it back from the dealership for a simple oil change or some such. It is especially noticeable under load (A/C clutch engaged, turning wheels while parked, etc). Past about 1500 RPM it's not noticeable, and acceleration is fine and dandy. The problem is generally worse when the engine is cold.

I've done quite a few (some probably foolish) things to try to fix it over the years - like replacing the engine mounts first. Here are some other things I've tried (and I'm probably forgetting a few):
- Replace the PCV valve
- Replace the MAF sensor
- Replace the upstream O2 sensor
- Replace Spark Plugs
- Replace Ignition Coils
- Replaced the intake hose (massive crack discovered from a cigar smoke test - I was really hoping this was it, but no dice)
- Drained and filled coolant, and massaged that upper hose to try to get the air bubbles out.
- Valve adjustment while the engine was cold (a first for me, and it actually got rid of a weird groaning noise I had when accelerating from a complete stop).
- Replaced serpentine belt and tensioner pulley
- Replaced A/C compressor

Yea - I went down some weird rabbit holes and spent a lot of money, but in my defense, it's been an awesome experience to operate on my own car.

Today, I went back to checking the vacuum (finally bought a vacuum gauge), and teed into the line for the fuel pressure regulator. After starting it up (cold), the gauge went up to about 16 inHg, then dropped down to 13 inHg - well below the "normal" green zone on my gauge. After this, the gauge gradually (over about a minute) creeped up to the middle of the green zone - roughly 20 inHg. I don't know if this is normal behavior (maybe related to the engine RPM changing), or if the computer started making some adjustments to get it where it was supposed to be because something was off. Would this indicate some kind of problem?

I was thinking about taking the vacuum hose off of the fuel pressure regulator to see if fuel comes out after it's removed. Then maybe buying some kind of scanner tool to get realtime diagnostic info from the engine to pinpoint anything off - not that I'd know what to look for?

Curious on any other thoughts to finally solve this issue. Thanks for any and all advice!

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5 months 2 weeks ago #201279 by hondaguy453
Replied by hondaguy453 on topic 2008 Acura RDX - Idle Issues
It does sound like a vacuum issue. I would suggest to check for vacuum leaks, especially because the issue disappears once. If it were a fuel issue the vehicle would exhibit loss of power through the whole power band instead of just the idle issue. I could not find the vacuum spec. in the manual I sent you, so you may need to buy one to find the correct spec's. The reading you got does seem a little low though.

If it ain't broke, don't fix it
A1, A6, and A8 ASE Certified

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5 months 2 weeks ago #201283 by TKB
Replied by TKB on topic 2008 Acura RDX - Idle Issues
Thanks - I guess it's time to finally buy some carb cleaner (and a fire extinguisher). Will report back with further findings in the next day or two.

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5 months 2 weeks ago #201289 by abdallahbill
Replied by abdallahbill on topic 2008 Acura RDX - Idle Issues
I have an 04 pilot that use to idle like crap. Replaced the radiator because it had a pin hole leak. Now it purrs... i remember Eric saying Honda's were sensitive air in the cooling system.

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5 months 2 weeks ago #201302 by relative4
Replied by relative4 on topic 2008 Acura RDX - Idle Issues
You might get lucky with a spray test, but the proper approach is a smoke test.

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5 months 1 week ago #201321 by TKB
Replied by TKB on topic 2008 Acura RDX - Idle Issues
I was hoping a drain and refill of coolant would help with the potential air-in-the-cooling-system issue, but nothing changed for me. Did you have fluid leaking out of the radiator, or how did you determine it had a pin hole leak? Currently I have no leaks (that I can find).

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5 months 1 week ago #201322 by TKB
Replied by TKB on topic 2008 Acura RDX - Idle Issues
I did the carb cleaner test real quick before the engine warmed up (what can I say, spraying it on a hot engine makes me nervous). No idle changes that I could hear, but I can't easily access all around the engine due to the intercooler placement.

I have to take the car in for an alignment since I just replaced the front lower ball joints and tie-rod ends, so I'll probably get the smoke test done at the same time. In the meantime, I'm going to stop by Harbor Freight and grab a Zurich ZR-13 to get some real-time engine data. I'll probably post a video of the data to see if it helps diagnose anything.

Thanks for all the responses so far.

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5 months 1 week ago - 5 months 1 week ago #201339 by TKB
Replied by TKB on topic 2008 Acura RDX - Idle Issues
Editing this because I think I got it backwards the first time around due to lack of understanding of the MAP sensor.

I got some live data, and checked some sensors both idle and driving around. I don't really know what I'm looking for, but general thoughts are below.

Parked and idle:
The car runs rich, and STFT hovers around -5% to -8%, sometimes going to 0% or -12%. The car shows barometric pressure of 29 inHg, and the MAP sensor shows 8-12 inHg, which would indicate a vacuum of -21 inHg to -17 inHg (I think - if I'm actually interpreting all of this correctly).

When accelerating, the MAP sensor (on the intercooler) goes as high as 55 inHg, which I assume is boost pressure from the turbo. I think this is normal?

Would the engine rich condition be enough to cause a rough idle?

If any experts want live data, I can record a video and upload it. 5 sensors can be shown on the screen at a time.
Last edit: 5 months 1 week ago by TKB.

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4 months 1 week ago #201774 by TKB
Replied by TKB on topic 2008 Acura RDX - Idle Issues
Well, a month has gone by and a new problem has come up - this one a bit more serious than the rough idle, although they could possibly be related?

The engine started making some weird whining noises that are audible in the cabin. They've gotten louder and louder. I thought maybe it was the power steering pump or alternator bearings starting to go. But, I was driving in a crowded parking garage yesterday when it felt very difficult to accelerate. I was about 2500 RPMs and the car was barely wanting to move. I started thinking I was going uphill and just couldn't tell, or it was possibly the transmission. By the time I left the garage it was back to driving and accelerating normally.

Today, I started the car up and the noise was a lot more prevalent. I didn't really have a choice on driving since I had to get to jury duty. The car made it there fine without incident, just odd whining from the engine that actually quieted down as it heated up.

On the way back I was at a stop light, and the whining suddenly stopped. The light turned green and I went to accelerate but it was barely moving forward - again about 2500 - 3000 RPM and I was slowly rolling through the intersection before it lurched forward, the whining noise came back, and it took off again like nothing was wrong.

I stopped at a Honda dealership to grab some ATF, and when I got home the dipstick showed it was at the bottom of the range for HOT, and the color was red, almost like new (I've had it replaced at least 2-3 times). Regardless, I put in about half a quart and let the car run for a while before checking it again - this time at the top of the HOT range.

The whining noise still persists and I'm getting hesitant to drive the car.

So transmission, or maybe the brakes are randomly locking up? Thoughts?

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4 months 1 week ago #201779 by relative4
Replied by relative4 on topic 2008 Acura RDX - Idle Issues
Video?
Have you still not smoke tested?

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