My idle is "throbbing"

MMT51 · Post by **MMT51** » 18 Jan 2013, 16:22

My 2000 S70 GLT SE with 138,000K has a constant oscillation in idle speed, about 835-870 RPM. Always, warm or cold engine.

There are no codes, no starting problems, none of the big RPM swings I read about with rough idles, hunting idles, etc. Just a steady up and down rhythm, with the extra vibration and noise. Here's the live data:
RPM c.830-870
Spark Advance 4.5-9.0 degrees
MAF .5-.6 lbs./min
TPS 1.6-2.7
STFT -2.3 - +1.6
LTFT 7.0

Car runs OK otherwise, but the varying RPMs probably continue while driving, just not as noticeable. It's making me nuts, now that most of the other maintenance and repair jobs have been done.

This car is driven 4-6K each year. Mostly short trips around town. Over the last 3 years I have replaced the following:

MAF and Purge Valve
Battery
Spark Plugs, Fuel Filter & Air Filter
Radiator, Thermostat & Hoses
Timing Belt, Water Pump, Idler & Tensioner
Alternator, Serpentine Belt & Tensioner
Pre Cat O2 Sensor
Vacuum Hoses from Purge Valve to Intake Manifold
Vacuum Hoses from Manifold to Brake Booster including Injector (Y-shaped valve)
Positive Battery Cables - Alternator to Starter, Starter to Battery, Battery to Fuse Panel

The Electronic Throttle Module is the yellow label replacement, just removed, cleaned and replaced with a new gasket. I spoke with Xemodex, and went through their diagnostic flow chart to eliminate that as a cause. At their suggestion, I replaced the positive battery cables (particularly the B+ cable to the fuse panel) and took it to the dealer for the recall upgrade of the ETM software. The dealer said my PCV system seemed to by OK.

I think I've eliminated the vacuum leaks. Did smoke tests with my homemade smoke machine and sprayed carb cleaner and propane all around the intakes, manifold, injectors and vacuum hoses.

Nothing has affected the wavering idle.

The injectors seem to be clicking away. Unplugging the MAF causes a really rough idle.

I haven't touched the 3 lines from the Turbo Control Valve or the TCV itself.

I don't have the gauges for measuring manifold vacuum and fuel pressure, so haven't done that yet.

I'm on the second bottle of Techron and considering sending the injectors out for service.

I'd appreciate any suggestions of where to look next. I've searched on this forum and elsewhere, but anything I've found regarding idle fluctuation seems to be much more extreme and associated with other starting and running problems.

Thanks to all on this forum for so much help. 138K used to seem like high mileage!

Peter

MMT51 · Post by **MMT51** » 20 Jan 2013, 21:42

Still working away at this. I found another vacuum leak, where the U-shaped plastic air pipe connects to the throttle. The pipe was worn in the last 3/4", where it contacts the ridges of the throttle body. Coating the inside with Permatex non-hardening gasket maker took care of the leak, but not the problem. The engine runs smoother and acceleration is better, but the idle still
fluctuates the same amount.

The spark plugs are NGK BRK6EIX Iridium, with about 7000 miles on them. They look normal, and all seem worn the about the same.

Has anyone had this? Were you able to cure it?

Post by **jblackburn** » 20 Jan 2013, 22:39

Is it bouncing around with this kind of frequency?

Also, keep in mind that once you fix vacuum leaks, etc., you should disconnect the battery cables and reset the computer. Let it learn to idle with proper air/fuel trim mixes.

Post by **precopster** » 21 Jan 2013, 05:08

The removal process of the ETM on a S70 GLT (or 2.4T in our market) isn't so roomy. I replaced one 4 days ago on a hot day and I was swearing so profusely that I could have made Darth Vader blush.

The ETM is like a sardine in a smaller can than a matchbox. For a first timer plan an all day event just to clean it.

I have new holes in my hands that are still healing. Getting it back in and lining up the gasket was a lesson in contortion that Houdini would have been proud of.

Coincidentally the ETM I replaced had none of the usual symptoms; this time it had hard cold starting and hard hot starting until the engine was on for over 5 minutes. The ETM had been cleaned well. The idle would not settle easily and I was most unconvinced the ETM was the fault. The owner had tried everything else and had given up. He DID have some ETM codes from time to time, though.

I used an '01 XC 70s ETM and refurbished it with a Sacer sensor. It was like a transformation after the job. No hard starts and perfect idle that settled quickly.

MMT51 · Post by **MMT51** » 21 Jan 2013, 14:32

jblackburn: I'ts not making wide swings, only about 35 RPM, but enough to feel a little rough and make extra noise. I tried the ECU reset and driving the specified cycle, with no change.

precopster:
Dealing with the ETM on this car is pretty miserable. The U-shaped turbo air pipe gets in the way of everything. My solution is to remove the top and bottom air hoses from the intercooler, undo the fan to fan shroud screws (remove the top two, loosen the bottom two), and move the fan down and over toward the battery. This leaves room to loosen the clamp on the air pipe and remove it from ETM.>

Post by **precopster** » 21 Jan 2013, 14:54

I did the removal in a similar way except I squeezed the fan totally out then removed the ETM with the pipe complete as I couldn't even spot the clamp. It's tight but doable. To replace it I made sure the clamp was in a position that could be accessed for next time.

To put the fan back in I flexed that pipe to what seemed like near breaking point before attempting the 4 bolts then pushed the fan over toward the battery as you did.

Long extensions on a 1/4 inch drive from underneath poked between the subframe to retighten.

To make the gasket stayed on I placed thread tape on the shoulder of one of the bolts; this kept the end of the bolt sticking out enough to stop the gasket from spinning around. One of the other bolts remains captive if you clamp on the pipe as you can't insert one of them once the pipe is on.

MMT51 · Post by **MMT51** » 21 Jan 2013, 19:40

I'm trying to figure out what to check next.

Fuel Injectors - send out for cleaning, new filters and o-rings? I spoke with Hurst Injector Service in Fitchburg MA about this. He told me pour in some Kroil to clean the valves while the injectors were being serviced. Perhaps carbon on valves has something to do with this.

Should I be checking compression and manifold vacuum? It doesn't seem like a fuel pump issue; the engine always starts, never dies or hesitates, just runs unevenly.

Post by **JimBee** » 21 Jan 2013, 20:49

MAF spec's in pounds per minute? I haven't heard of that. Rolling engine speed could definitely be caused by a bad MAF. I would do an electrical eval. There are a couple of posts on this site that are detailed with pictures for the '98 I think. Your voltages might be a little different, so you'll want to confirm them. You can do it with a multimeter. If voltage output is a little erratic it could cause your symptoms.

Post by **jblackburn** » 22 Jan 2013, 07:42

I agree - sounds like an electrical problem, and the MAF would be on my (very) short list of things to check out.

MMT51 · Post by **MMT51** » 22 Jan 2013, 11:03

JimBee, jblackburn - thanks for thinking about my problem.

Jim, found your post on testing the MAF.

https://www.matthewsvolvosite.com/forums ... e+#p251289

Exactly what I was looking for, will do it today.