190D 2.2 Low Idle and No Tach - PeachParts Mercedes-Benz Forum

DieselPaul · #1 03-01-2014, 09:50 AM

For those who have read my other threads... it has happened again, but to a different car.

Just bought this 1985 190D 2.2, my dad has put 1300 miles on it in a month. We needed a spare car for the winter while other cars were put away or broken so I went out and bought this car. 280k runs and drivers really well.

Car was idling great and the tach was working. My dad brought it up from Cincinnati to Columbus for brunch and we decided to throw some fuel filters on it because I had no service records for the car and the prefilter was black. Took the air cleaner off to get to the prefilter and replace any seeping lines. Put back together, primed the spin on with ATF. Started right up, but was idling low and had no tach. Drove it around the block, no change.

He had to drive it back to Cincinnati, and put 500 miles on it with the low idle and it has not fixed itself, nor gotten worse.

He came up this weekend and I tried to fix it:

Cleaned all the connections I thought were related to the ELR.

Tried 5 OVP relays

Tried an unknown ELR relay (just bought another spare on it eBay I'll try next time I see the car)

Tried the crank sensor out of my wagon

Fuse 10 (tach and emissions fuse) is good, put in a brass one for good measure. Have power on both sides of the fuse.

Opened up all the connectors for the OVP and ELR and tightened the metal part of the connectors so they would not be loose connections.

Pull the airbox back off and looked for any pinched or squeezed wires, did not see any

Cleaned the battery terminals, the ring terminals from the alternator, and both main grounds.

It has to be something I damaged when I was working on the car. I took the airbox off, and I also pulled the cowl off to get to the heater control valve to pull vacuum on it (heat is stuck on)

So what could have damaged or unplugged?

Which connection on the injection pump itself is related to the idle control?

I've read people talking about "tone-ing out" wires to test to make sure a wire in the harness has not broken, what is a good way to go about that?

I am thinking maybe the 30 year old harness exposed to 280k miles of heat is brittle and maybe I broke a wire or something that is hidden in the harness.

I'm stumped, but mostly annoyed because I know its something I broke haha.

Any thoughts appreciated. Thanks!

Diesel911 · #2 03-01-2014, 10:21 AM

Black stuff in the Primary/Plastic Filter usually indicates something is growing in the Fuel Tank. So that is another item that needs taking care of.

vtmbz · #3 03-01-2014, 10:31 AM

Doesnt the egr get a signal of some kind from the back of the injector pump? If not, there are a lot of vacuum junctions below the airbox and god only knows, its a tight squeeze.

DieselPaul · #4 03-01-2014, 11:34 AM

Quote:

Originally Posted by Diesel911

Black stuff in the Primary/Plastic Filter usually indicates something is growing in the Fuel Tank. So that is another item that needs taking care of.

He ran a few tanks of fresh fuel through it before we changed the filters and 400-500 miles later the prefilter is still clear. I'll keep an eye on it, but that isn't causing the main issue.

I unplugged the EGR the day I got it and capped off the vacuum line, it ran for a long time with working tach and the correct idle. I temporarily hooked all the EGR back up and it did not change anything.

ah-kay · #5 03-01-2014, 11:58 AM

How do you know idle if low if tach is not working? The tech circuit is also controled by the Kilma relay. Did you move or dislodge it? This is link you may be interested. Read thru the whole post, especially #15.

'84 190D, EGR Module..???

DieselPaul · #6 03-01-2014, 12:04 PM

I can hear the low idle, and it shakes a little more than it ever did. It idles lower than my 200TD, 190D 2.5 and and 87 300D. It was running for 3 weeks before this happened, the difference in RPM is noticeable.

That was a good link, I have some reading to do in there.

I tried two Klimas with no change. It sounds like the A/C compressor is part of the circuit, and on the 601 I am pretty sure the A/C wires run in between the Power Steering Pump and the Air Box. Maybe I pinched those wires, I didn't do a thorough inspection of the A/C wires as I didn't realize it would be related.

vtmbz · #7 03-02-2014, 08:13 AM

My last 190d idled slowly until it warmed up and then speeded up when it got to operating temp; that is, backward. One of my canadian friends told me it was because I had a wire socket plugged in backwards on a temp sensor and if plugged in correctly would reverse things; I never got it sorted out, but it might be relevant to your problem.

DieselPaul · #8 03-02-2014, 09:52 AM

When its below 32* the car actually idles higher and when it gets to temp the idle drops down.

vtmbz · #9 03-02-2014, 09:19 PM

I would say its more likely engine coolant temp that matters, but still that part of the idling sounds like its mostly functioning. It points to a vacuum circuit as the culprit but Im only guessing.

ROLLGUY · #10 03-03-2014, 12:25 AM

Does your car have an electric or vacuum idle control? (my guess is electric). The back of the IP will have either a solenoid, or a vacuum pod. If vacuum, the hose goes to a switchover valve on the firewall. If electric, the solenoid is directly on the back of the IP. You should be able to test either one by applying 12v to either the solenoid, or the switchover valve. If vacuum, just connect a vac tester to the pod. On both models, there is a lot of hoses running all over the engine bay to different components. You might have broken one of the plastic vac lines (very easy to do) when working on it. Believe it or not, I was working on a 190D 2.2 just the other day and had/have the exact same problem. I broke so many plastic lines working on it that I just disabled all the vac equipment except the shutoff and the VCV for the auto trans (yuck!). I still have to make the vacuum idle control work.....Rich

pawoSD · #11 03-03-2014, 09:06 AM

The om601 does not have an electric idle controller at all, it has a vacuum adjuster that can raise the idle by about 100RPM when the A/C is on....that's it. The idle is mechanically set, and can be switched between "normal" and "raised" by applying vac to the little solenoid on the IP. On mine I plumbed the line to be always under vac to keep the idle higher just because its smoother at 750rpm than 600-650ish.

DieselPaul · #12 03-03-2014, 09:33 AM

Then what does the ELR do on a 190D?

Sorry for the short reply I'm posting from a phone.

I was hoping you'd chime in pawo as you've done a swap.

The next question is why did the tach go out at the same time? The motor definitely idles lower than it ever did before, you can tell by the shaking and just by listening to it.

It sounds like when the OVP died on my 87 and the ELR died on my 92. Its definitely not idling right. When the car cold in the morning it will idle smooth at a noticeably higher idle. After a few minutes once it warms up the idle drops down real low.

pawoSD · #13 03-03-2014, 09:48 AM

I believe on a normal 190d 2.2 the ELR controls a switchover valve to the vacuum idle adjuster I mentioned. Normally that would be off/no vacuum though unless the A/C is on....maybe the mechanically set idle is too low....mine idles rougher with the vac adjuster disconnected. I think the Tach is also driven by the ELR. My car doesn't have those circuits (I have no tach either) so I am not entirely sure.

DieselPaul · #14 03-03-2014, 09:57 AM

Well I was replacing a lot of vacuum connections trying to get the heat to turn on off. Maybe I created a leak somewhere. I have a friend with a smoke machine, maybe Ill get together with him.

Do you guys think my dad is doing damage to the car idling at 500rpms? I can't see why that's a problem but his coworker assures me I am causing serious engine damage for reasons he can't explain.

The car still shifts as well as it did before so if I created a vacuum leak it would have to be on the other side of a check valve or switchover wouldn't it?

pawoSD · #15 03-03-2014, 12:31 PM

Idling low won't hurt it, it will just vibrate more....