1999 E300 idle fluctuation - Page 2 - PeachParts Mercedes-Benz Forum

packerfan · #16 05-21-2017, 11:23 AM

Quote:

Originally Posted by jake12tech

It can't be adjusted, only replaced. It's electronic, sometimes they go bad.. I've seen a few on w210s that were bad. All gas cars, but the same concept applies. Mine is made by Foseal for android and iPhone.. I found it on Amazon for $20 and that's more than I paid. I'd try eBay, last time I looked that one that I have is cheaper on there!

Before ordering any parts, make sure to scan it first for pending codes.. It'd be a waste to order it and not be the TPS. But we will go from there once you get the scanner.

BTW, my 99 E300 started doing this since the glow plugs went bad.. It's really nothing to be too worried about, I've been living with this for quite some time.

If the motors hot, and you go to start it again it will go back up to 7-800RPM right? That's what mine does.

I finally got a chance to register my new (to me) '99 E300 and take it out for a drive. It started right up with the fresh glow plugs that you helped me with (can never thank you enough for that valuable experience) and idled around 800-900 RPM but when I put my foot on the brake pedal the idle dropped to 600. I put the car in gear and went for a 10 mile ride. The first mile or so I was followed by a cloud of smoke but that slowly cleared up. As I was driving I would touch the brake pedal and the RPM's would drop and then go back up as soon as I took my foot off the pedal. this is not something you can feel but I found that to be interesting, I'm guessing that is normal?
When I got home I let the engine idle and there was very little oily/diesel smelling smoke coming out the tail pipe.
The engine is "nailing" and so does my '95 but that comes and goes on both cars. I did get ahold of Greazzer and he is going to rebuild my injectors, hopefully that will take care of the nailing and slight smoke at idle.

jake12tech · #17 05-21-2017, 12:29 PM

It's also a combination of winter fuel with lower cetane... mine was nailing all winter and now it doesn't nail at all. Add cetane booster. Also, glad to hear about the plugs as well. I'd love to see a video of your rpm fluctuation. RPM will drop and raise if you have a lockup torque converter. I believe these cars do have lockup converters. They're for fuel economy. They also have a fifth gear overdrive. That's why low rpms at 65mph

engatwork · #18 05-21-2017, 02:29 PM

I've got one in the shop that revs up sometimes when you shut it off.

packerfan · #19 05-21-2017, 08:47 PM

Quote:

Originally Posted by jake12tech

It's also a combination of winter fuel with lower cetane... mine was nailing all winter and now it doesn't nail at all. Add cetane booster. Also, glad to hear about the plugs as well. I'd love to see a video of your rpm fluctuation. RPM will drop and raise if you have a lockup torque converter. I believe these cars do have lockup converters. They're for fuel economy. They also have a fifth gear overdrive. That's why low rpms at 65mph

I'm having trouble uploading video of rpm dropping when touching brake pedal while driving on highway.
I can tell you that driving 70 mph the rpm is at 2500 and if you touch the brake pedal rpm's drop off to approx. 1000.and go back up somewhat when you take your foot off the brake pedal.
The fluctuation I was experiencing in the beginning was when the intake was removed to change glow plugs and I would let the engine run to get it hot.
Now that the intake is back on everything seems to be fine.

jake12tech · #20 05-21-2017, 10:28 PM

So this went away now that the intake is back on? I'd really have to see a video to understand. I think if I touch my brake pedal does the same thing on my w210s... I think it may be normal, it could just be the trans downshifting. I'd really have to see.. Try youtube upload and you can post the link on here.

packerfan · #21 05-22-2017, 10:24 PM

Quote:

Originally Posted by jake12tech

So this went away now that the intake is back on? I'd really have to see a video to understand. I think if I touch my brake pedal does the same thing on my w210s... I think it may be normal, it could just be the trans downshifting. I'd really have to see.. Try youtube upload and you can post the link on here.

Here you go:https://www.youtube.com/watch?v=6pCnHOXi118
When intake manifold was off engine would creep up to 900 rpm and when I would rev the engine a few times it would go back down close to 600. Now that new glow plugs are in and intake is back on things seem to be normal.

tjts1 · #22 05-23-2017, 12:15 AM

Your idle RPM is too high but it goes down to normal idle RPM when you press the brake pedal. I wonder if you have a vacuum leak in your brake booster thats affecting the waste gate actuator or some other actuator like the EGR valve.

packerfan · #23 05-23-2017, 09:51 AM

Quote:

Originally Posted by tjts1

Your idle RPM is too high but it goes down to normal idle RPM when you press the brake pedal. I wonder if you have a vacuum leak in your brake booster thats affecting the waste gate actuator or some other actuator like the EGR valve.

The engine RPM will slowly creep up to around 900 and go down when I press the brake pedal.as soon as I take my foot off the pedal the RPM's creep up again.
I'm trying to find a tech article somewhere that shows how and where to test for vacuum leaks.

tjts1 · #24 05-23-2017, 10:51 AM

Temporarily disconnect the vac line to the brake booster, cap it off and repeat the same experiment. Also take a close look at the line going to the brake booster for cracks breaks.

packerfan · #25 05-24-2017, 10:16 PM

Quote:

Originally Posted by tjts1

Temporarily disconnect the vac line to the brake booster, cap it off and repeat the same experiment. Also take a close look at the line going to the brake booster for cracks breaks.

I'm having a hard time figuring out how the vac line to the brake booster is attached. Is the line you are referring to ridged and approx. 1/2" in diameter going from vac pump to brake booster?

KarTek · #26 05-25-2017, 07:05 AM

The ECU on these cars is programmed to override the TPS when the brake pedal is pressed for safety reasons (Toyota could take a lesson here).

If the TPS is running artificially high due to a malfunction, it makes sense that the car would return to a normal idle when the brake pedal is pressed.

Murkybenz · #27 05-25-2017, 08:38 AM

A vacuum leak will not increase revs on a diesel.
On a diesel you give it fuel to increase revs .
On a petrol engine you control the air going in and the system adds the fuel for that air flow, so a vacuum leak will increase revs.

packerfan · #28 05-25-2017, 10:01 AM

Quote:

Originally Posted by Murkybenz

A vacuum leak will not increase revs on a diesel.
On a diesel you give it fuel to increase revs .
On a petrol engine you control the air going in and the system adds the fuel for that air flow, so a vacuum leak will increase revs.

Hmmmm......so what is causing my engine to idle too high, what regulates the idle speed?

jake12tech · #29 05-25-2017, 05:40 PM

Pretty sure idle speed is electronically controlled by your governor on the pump. The pump is half mechanical half electronic.

KarTek · #30 05-26-2017, 09:10 AM

Check the basics, make sure the throttle cable isn't too tight, not allowing the TPS to return to full stop.

The adjustment is right there at the TPS, couldn't be easier.

When I first got my car, the cable was really slack, causing a noticeable softness in the pedal. I dialed it in tighter, which improved things but I did notice that it was easy to get too tight and overcome the return spring on the TPS.

Which makes me think; I believe there are 2 springs on the TPS. Make sure one hasn't broken. I'm just going off memory but I think they are nested inside one another.