Idle runs high and settles slowly

**racer2086** · 12-01-2019, 02:43 PM

This has been bugging me for some time, but now needs some real attention with my new transmission.

Whenever the A/C is on, the DME increases the idle as expected. But after the car is fully hot and driven around, the idle tends to hang up a little higher than when the A/C is first turned on. Additionally, if you rev it up, the idle will drop back down but slowly. At a light, the car is really pushing to go forward. Lastly, it is causing a hard downshift from 2 to 1 when coming to a stop that makes the transmission kick into 1st gear. Hard. It's like the engine is running too fast.

Here's what's been done:
I smoke tested the car and found a leak where the boot hooks to the resonator. Fixed now with a new tube. Re-smoke tested and no leaks.

New air filter

I replaced the TPS with a new one due to also having weird throttle behavior...it's hard to hold the rpms consistently at a speed anywhere below 1100 rpm. The throttle felt "on" or "off". I measured it and it read 1.28 kohms and 4.3 kohms. So I replaced it but the new one actually reads a little worse. No difference in how it drives but I may try another.

Checked accelerator cable linkages and all are ok. I can wiggle them at closed throttle so they are not holding open the throttle.

Cleaned the ICV.

Not really sure what else to do?

- - - Updated - - -

Edit: can the ICV be slow to respond or staying open even if it is clean and flops around no problem?

**goinstrong** · 12-01-2019, 03:14 PM

Try spraying the MAF with MAF cleaner...

**racer2086** · 12-01-2019, 10:34 PM

I will try that, but I don't think it's the maf.

When I pull the dipstick, the idle increases 50 rpm before readjusting. There is mild suction on the dipstick if I put my finger on it. I know a lot of suction is a bad CCV, but is a little suction normal? Maybe the CCV is starting to go bad and causing a vacuum leak? I don't see smoke, but the car has been using 1qt of oil per 3000 miles, but I attributed that to high miles.

Also, most of this idle issue is coasting, as the car downshifts. It hangs up around 1000 rpm and drops as the car brakes. It's almost as if the brakes through the transmission are bringing the idle down. The idle will settle down to normal with the car in gear at a stop, it'll pull down. Putting the car in neutral or park will cause the rpms to jump up before settling back down via control of the ICV (this may be normal not sure).

**racer2086** · 12-01-2019, 11:40 PM

Should also add that this is mainly just a problem when the A/C is on. When off, the rpms are lower and I don't feel the 2 to 1 downshift.

**Timm** · 12-02-2019, 05:57 AM

The two main causes of high and poorly-controlled idle is MAF and vacuum leaks - the vacuum leaks can be tested for with INPA:

The MAF can only really be tested by putting ina new OEM one!

**racer2086** · 12-02-2019, 12:01 PM

Timm! I was using your site for guidance on this. Incredible the amount of info on these adaptation values. Haven't seen that before, and now I understand it for the first time!

The main reason I am posting this is due to the hard 2-1 downshift I feel in the transmission. I am not suspecting the transmission because it is brand new with less than 10k miles on it. The hard downshift is 10x worse with the A/C on (I am assuming due to the higher idle).

I fixed the vacuum leak at the MAF boot a good hundred miles ago, but did not reset any adaptations. I'm attaching my INPA screen for reference, as this is how the car is running now. The additive values are a little high, but I think would be worse without the multiplicative value adjustments. Bank 2 is higher on the multiplicative. This is what it looks like just idling with A/C on.

Pulling the dipstick causes the lambda values to increase due to the extra introduced air.

Here is the INPA screen when I disconnected the MAF. The lambdas went way down, which may be an indicator that the MAF is registering more air than it should be?

How do I know if the CCV is also leaking? It's about 3 years old with 50k+ miles on it. I looked into the intake when I pulled the ICV to clean it and it appeared damp with oil (not full of it, but a film of oil for sure). Car doesn't smoke, but does consume oil at least a quart or two between my 7500 mile oil changes. I switched to full synthetic to hopefully reduce that.

There is some suction at the dipstick and I can hear a gurgling when I pull it, which seems abnormal. There is about a 50 rpm increase in idle and it gets rougher when the dipstick is pulled and putting my finger on it reduces it immediately. I can feel suction but it's not insane. When the dipstick is in, there's a loud hissing noise inside the intake, which I assume is just the air rushing around. When the dipstick gets pulled that noise becomes sputtery or goes away significantly.

Should I just replace the MAF and CCV? I'll clean the MAF right now and see what happens.

**goinstrong** · 12-02-2019, 01:41 PM

You may already know this little trick for the CCV repair, but just in case you haven't seen this:

https://www.youtube.com/watch?v=-VJbQbLARkg

It is SIMPLE, and took me maybe 10 minutes start to finish. I had rough idle, blue smoke on startup, and it blew blue smoke on the freeway. This solved all of those issues, and the car has 14,000 miles since the replacement. Uses NO oil. It is now my son's car, so I see it often. Hope this helps!

**Timm** · 12-02-2019, 03:35 PM

The adaptation values look fine - but the disconnected MAF values certainly look a bit askew! You probably have tiny vacuum leaks - very unlikely to be the PCV valve, they generally let a lot more air in than that. Certainly worth changing the MAF with an OEM one.

I had those awful changes on one of my my 740i's - and that was the MAF

**racer2086** · 12-02-2019, 05:36 PM

Timm, I smoke tested the car the other day and found the leak at the resonator. Replaced that connecting tube and tested again. There was no smoke anywhere. I will test again tonight when I get home.

Just an update. I went home at lunch and sprayed the MAF down with MAF cleaner. Sprayed it dry and clean with compressed air. Installed it and went to drive the car after lunch and now starting it up it will rev and stay at 1000 and creep up to 1200 rpm. It will not idle down now at all. So either the MAF is really bad or I really screwed it up now.

When pulling the plug to the MAF, the car will drop right down and almost stall before catching itself and idling back up. It will then hunt up and down as the ICV tries to stabilize the idle. I didn't let it go long enough to see if it would stabilize fully. I pulled it back in the garage and drove the ZHP back to work to not be late. So it seems the MAF is bad. I just don't understand how it doesn't throw a check engine light. Weird.

I will leave the CCV alone and replace the MAF.

**rslifkin** · 12-02-2019, 06:56 PM

Originally Posted by racer2086

So it seems the MAF is bad. I just don't understand how it doesn't throw a check engine light. Weird.

Sometimes you can end up with a sensor feeding bad data, but relative to what the engine is doing and other sensors are seeing, it's not obviously bad in a way the computer picks up on and complains about.

**Mayorchuck** · 12-02-2019, 10:12 PM

It's been my experience, on the forum anyway, that the MAF rarely throws a code when it is bad. I experienced the hard downshift when mine went bad as well.

**racer2086** · 12-03-2019, 09:25 AM

So unfortunately, it looks like there isn't much of an OE option other than the Genuine BMW part at $440.

That's a little crazy of a price for a sensor that seems to go bad every . Anyone have a source of the OE Bosch one that I bought before?

FCP has no listing for it and can't get it, ECS says it is backordered, and OEMbimmerparts only has a Delphi sensor to install in the old housing. Strongly considering giving the $20 sensor on Amazon Prime a shot

since it'll be here by Friday, it's returnable, and $20 is a worthwhile experiment.

This most recent Bosch sensor only lasted about 5-6 years, and I think has been bad for at least a year.

**purplecty** · 12-04-2019, 07:14 PM

I may have a used one sitting around that i changed preventatively as i sold my 98 a few years ago. PM me you address and I can try and ship it out to you this weekend to test...
They aren't cheap and most NLA for new ones...

https://www.ecstuning.com/b-bosch-pa...3621702078~bo/

**gaspump** · 12-04-2019, 08:08 PM

You might try looking at your carpets or floor mats. Seriously, I had my idle go up and stay up, then slowly come back down. I pulled the rugs back and the idle came down. The mats were pushing against the has pedal.

**racer2086** · 12-04-2019, 10:18 PM

Originally Posted by purplecty

I may have a used one sitting around that i changed preventatively as i sold my 98 a few years ago. PM me you address and I can try and ship it out to you this weekend to test...
They aren't cheap and most NLA for new ones...

https://www.ecstuning.com/b-bosch-pa...3621702078~bo/

Thank you. Will PM now. I even tried advance Auto and AutoZone who had them listed on their site, but each checkout threw errors that they're unavailable. It crazy that Bosch is so backordered.

Originally Posted by gaspump

You might try looking at your carpets or floor mats. Seriously, I had my idle go up and stay up, then slowly come back down. I pulled the rugs back and the idle came down. The mats were pushing against the has pedal.

Great thought but the carpets are definitely not the issue. The idle changed drastically just unplugging the MAF.

**Mayorchuck** · 12-04-2019, 11:13 PM

Edwin always said not to unplug them when the car is running. The one time I did the car just died. Have you tried driving it in default mode, with the MAF unplugged?

**racer2086** · 12-05-2019, 03:29 PM

Originally Posted by Mayorchuck

Edwin always said not to unplug them when the car is running. The one time I did the car just died. Have you tried driving it in default mode, with the MAF unplugged?

Actually no I did not. It was idling so high, I just pulled it in and took the other car. I guess I can try that tonight.

**racer2086** · 12-08-2019, 03:33 PM

So my Amazon sensor came on Friday.

I decided to start the car today with the old sensor in anyway just to see, and to my surprise, it started and idled fine. It's possible it needed to dry out longer after I sprayed it with MAF cleaner.

Anyway, I decided to put the Amazon MAF in anyway just to try it out. The car didn't like it at first but adapted and smoothed out. The I would say not much changed with how the car idled down, but the down shifts seemed a little less harsh. I drove it a little while having my laptop hooked up to watch the values. I took videos comparing the two MAFs. The lambda adaptations went very positive which was strange. The MAF voltage was lower (3.2v at idle in park) with the Amazon sensor, like it was reading less air.

Then I put my old, cleaned Bosch back in and drove it and took a video. The idle responded similar to the Amazon sensor, but the lambda reading went way negative compensating for how they went up with the other sensor. And the MAF voltage reads about 3.5v at idle in park (before cleaning it was 3.8v to 4v). The downshifting feels very similar with my old sensor vs the Amazon sensor.

Basically, coasting down foot off the gas, the car will coast down to about 900-1000 rpm and then downshift into 1st gear. That's when you can feel it and the RPMs jump back up to about 1050-1100 rpm. The car will very slowly coast back down to idle. Almost as though it has a tailwind or your foot is lightly on the throttle. It takes time.

My theory is that the 2-1 downshift is harsh (and when I say harsh, you can hear a knock as it shifts down, feel it in the shifter, and get a mild kick in the car) because 1) either the car is downshifting too soon or 2) the rpms aren't dropping down enough before the downshift. It's like with a manual if you heel-toe downshift, but blip the RPMs too high you feel the kick when you let out the clutch. This would seem to make sense considering the car hangs around 900-1000 rpm while coasting with foot off the brake when it downshifts. I would expect it to coast down quicker before the downshift. I am not sure if this is something determined by the DME or also with input from the EGS or what.

My next question is...
Should I clear the engine adaptations with the now cleaned MAF and also clear the transmission adaptations?

The reason I ask this is that back when my transmission died, the shop down by my parents' pulled my transmission and sent it to Eriksson to get rebuilt (I wanted my original rebuilt). After 2 weeks of running my original rebuilt transmission, my parents said the transmission started clunking into gear when it shifted. I told them to bring it back and the shop took the car back for another month or so while trying different valve bodies from Eriksson and resetting adaptations etc etc. They did not want to flash the EGS with updated software for fear of bricking the module (it's got 1997 software on it; DME was updated/flashed in 2000). Nothing could solve the clunking shifting. So ultimately, the shop asked Erkisson to send another unit (they didn't want to tear it open) and they installed a whole new transmission, valve body, and torque converter. This solved the clunking when shifting into gear.

What I don't know is if they reset the adaptions after installing the new transmission, and if they did, it was adapted to my old "pre-cleaned" MAF. Secondarily, could they have changed settings regarding the idle while trying to get the old transmission to stop clunking?

A further note...if transmission is in sport mode, the hard downshift does not happen.

**Timm** · 12-08-2019, 05:44 PM

Your experiment just proved that the cheap MAF just doesn't measure the air properly at all!

**racer2086** · 12-08-2019, 08:44 PM

Originally Posted by Timm

Your experiment just proved that the cheap MAF just doesn't measure the air properly at all!

Yes! Which is why I'll be returning to Amazon!

Timm thoughts on wiping transmission adaptations to fix the harsh downshift? Not sure my MAF is bad, but I'm getting another from a forum member.

**racer2086** · 12-11-2019, 05:58 AM

I wiped the engine and transmission adaptations with my now cleaned MAF. Not much of a difference... Maybe a slight improvement.

The biggest problem I can describe as this...
Let's say you're driving along and you just let the car coast down, it will coast down to about 900 rpm in second gear and then downshift to 1st. Bam. BUT then the car will continue coasting along in 1st gear at 900-1000 rpm. At one point it sped up to almost 1100rpm like the car was driving itself! If I lightly put my foot in the brake I can slow the engine down to 700 rpm and it will stay there.

WTF is the deal? This is driving me crazy. It was doing this before the transmission died because I remember feeling the car was fighting stopping (that's that tendency to run on).

Is this just a MAF thing? Bad IAC? I'll replace whatever it is, but don't want to throw parts at it, especially because they're so expensive.

**rslifkin** · 12-11-2019, 09:49 AM

Vacuum leak maybe?

**racer2086** · 12-11-2019, 05:50 PM

Just replaed the TPS with another new one this morning. Also re-smoke tested the car with throttle wide open this time and there are zero vacuum leaks. It is definitely not a vacuum leak.

The hard down shift is far worse with the car fully warm. This morning it was virtually perfect at the beginning of my 10 mile drive, but hitting harder by the time I arrived at work. I was hopeful that maybe the TPS was the improvement, but nope. And the ohm measurements were the same as the other one.

At this point it I feel like it is either the MAF, IAC, or (and I have to check this) maybe the transmission is reading the wrong fluid temperature.

**goinstrong** · 12-11-2019, 07:01 PM

I may have missed it, but have you cleaned the IAC with brake cleaner? Also, spray the air intake temperature sensor with brake cleaner. (that solved my trans failsafe mode, and it also solved my low idle on my X5) However, it sounds like the IAC to me: the hanging and then dropping down. I would have said MAF, but it sounds like you have that sorted out.

**racer2086** · 12-12-2019, 06:20 AM

So, yes, I cleaned the IAC. Before it was still floppy, but after cleaning was super floppy.

I spent some time last night testing various scenarios.

First, the reason for the hard downshift is due to having a foot on the brake when the downshift happens above 900 rpm. It kicks because the car wants to take off due to the higher engine speed but the output of the transmission is held by driveshaft and brakes. This is evident because it kicks less if allow to roll into the downshift (but still not smooth).

With A/C on and engine cold, everything is smooth and downshifts fine.
With A/C off, everything is smooth and fine no matter the engine temp.
With A/C on and the car driven for about 10 minutes, the car progressively hangs above 900 rpm when the transmission downshifts into 1st giving that kick in the transmission as the car wants to "run on".
Unplug the IAC, no hanging and the car downshifts fine and feels normal. Idles at 700 rpm with the A/C on, but also 700 with A/C off (it should be 600). It also struggles when you just let off the throttle.
Transmission is reading a temperature of about 189 degrees F when fully warm. Car is at about 210 F.
Air intake temp measured as high as 140F.

Maybe next is drive without the MAF connected and see what happens.
Then clean that air intake temp sensor.
Otherwise maybe the IAC is getting stuck somehow?

It is so related to A/C being on and engine at full temp. I don't understand why it would be acting different.

I'll have to post up some screenshots and video.