Lumpy / Sensitive Throttle At Low Revs

[supersub14 1]

I posted this question on the 405 Mi16 forum but theres not much life on there so didnt get much help.

 

My 2.0 405 Mi16 is a bitch to drive slowly in traffic jams for example. Its fine otherwise.

 

Seems to be that when the car has very low revs and im following slow moving traffic in first gear that i need a lot of clutch + throttle action to keep the ride smoothish.

 

I had it in the garage last night and had her ideling. Sat nicely at approx 1000rpm. With the slightest touch of the throttle she jumped up to and above 2000rpm. Just seems to be really hard to find that bite point between 1000 and 2000rpm. Pedal seems to be ultra sensitive at low revs if you know what i mean.

 

If i try hard enough i can get her to idle in the 1000-2000 range. But i noticed that if i hold the throttle open at 1500rpm (for example) and dont move my foot, the revs hunt up and down from say 1400-1600rpm (maybe even more).

 

Obviously this problem doent bother me while im cruising down the motorway, but if i could sort out some way of getting more control of the lower revs it would be a far nicer car to drive.

 

Ive been told to check the coil and leads for stray sparks etc and they are fine. New leads fitted a year ago.

 

Also told that it could be a number of other reasons for such behavoiur of the car, including worn engine/gearbox mounts, worn clutch, or even just going up or down hill when the angle is not noticeable. But as car still does it while sitting on a flat garage floor this isnt the problem.

 

Any other ideas or should i just live with it??

[welshpug 1,657]

I would check the Throttle position sensor and the Lambda sensor

 

It should idle under 1000 rpm when warm.

 

engine mountings in a known good condition?

[supersub14 1]

how would the engine mounting affect it if the car is stationary? Unless you mean there is vibration from the engine affecting it?

[welshpug 1,657]

ahh I didn't notice you said it does it at a standstill as well!

 

I'd try the earlier suggestions, it sounds like the ECU isn't getting a consistent signal from something hence the varying revs.

[Miles 331 1 Cars]

Silly point but 2.0 Mi's don;t have leads, Only coil packs

[24seven 104]

Check for air leaks on the inlet as any unmetered air can send the ECU haywire at idle.

[supersub14 1]

ok cheers

 

ill look into those first and see what happens!

 

Have to do a search here now to find out where sensors are and how to test them

Edited March 4, 2010 by supersub14

[DrSarty 90 1 Cars]

Have to do a search here now to find out where sensors are and how to test them

 

You may struggle as they are a bitch to get to on that engine.

 

The TPS and IAT sensors in the throttle body are underneath/at the back. The plugs for them are at the front and on the top. Why oh why oh why?

 

Likewise, the ECU coolant temp sensor is underneath the water housing on the side of the head.

 

It's a c*nt it truly is!

 

Checking for leaks in the inlet hosing should be easy, and the hose can actually slip off of the throttle body, so that's what I'd check first.

 

I'd also check the MAP sensor tube which goes from the front of the inlet plastic manifold (centrally) to the ECU. Pop it off the inlet and blow down it listening/feeling for leaks before it gets to the ECU. In fact it may have come off the ECU, but unlikely.

 

BTW the lambda unplugs via 2 JPT connectors, one red and one white, quite near the ECU.

 

I bet it's something simple, and in another (For Sale) thread (GKZ or something breaking a 405), I've offered you a source of TPS, throttle body and coil packs if you ever need them and GKZ can't help. I have a couple of each.

Edited March 4, 2010 by DrSarty

[supersub14 1]

lol thats a lot of info to digest Dr Sarty in one go so ill work through it step by step I dare say ill be in touch for bits!!

 

I was on service box looking for where the lambada and TPS sensors were while you posted that

 

Can somone confirm that the Lambada is: 01 / 02

 

 

And throttle position sensor is: 31a (reheating unit)

 

 

Cheers

Edited March 4, 2010 by supersub14

[welshpug 1,657]

you need to check if you have a single plug or two plug Lambda connection, on a 405 they are in front of the battery tray on the PH2 and have a very long lead, most likely top be the two plug arrangement which is part #1

 

throttle position sensor is listed with the ecu, as the name suggests, that is a heater element you have outlined

[supersub14 1]

Check for air leaks on the inlet as any unmetered air can send the ECU haywire at idle.

 

will do. Although at idle it doesnt seem too bad. Worth checking anyway!!

[supersub14 1]

Cheers WP! I just see plugs and assume is sensors lol

 

Ok so ive been in at the engine tonight and noticed a few things strange (they may be normal but i cant tell)

 

Firstly, I checked for air leaks and i came across this pipe that comes from the oil filler cap:

 

 

Ive circled the part that concerns me. Is this broken or is it meant to be like this? Heres a better photo:

 

 

 

It just seems to push into the larger pipe but its not totally sealed up. The larger pipe comes from the air box so is it just a breather pipe? Or should no extra air be getting in here?

 

Secondly, ive been trying to find the sensors yous have mentioned. Ive checked haynes manual but it doesnt show any photos for the 2.0 Mi16 engine (basterds! ) so im gonna need a little help.

 

The yellow plug in the photo below is just hanging loosly on the throttle body:

 

 

 

Is this ok? Should it be mounted to summit? Whats it for anyway?? The two wires still are connected to the back of it and go out of sight behind/below the TB.

 

Finally, is this the TPS and IAT sensor on the TB that Dr Sarty was describing:

 

 

A = IAT

B = TPS

 

Thanks

[welshpug 1,657]

that oil breather should be firmly attached, but the takeoff has broken off, it wont cause any issues though.

 

yellow plug is the throttle body heater, grey the IAT, 3 pin plug for the TPS.

[DrSarty 90 1 Cars]

yellow plug is the throttle body heater, grey the IAT, 3 pin plug for the TPS.

 

Surely what I typed wasn't that confusing?

 

On the second bit, as I mentioned before, the plugs for the sensors are on the top and front; the sensors themselves are underneath or at the back. You would have to remove the TB (3 bolts) to get at them. Those pictured above are the plugs, not the sensors. It's a sh1te design.

 

Did you try the MAP tube test?

 

Your inlet hosing looks OK (if a little grimey) but have you found any splits?

 

The yellow connector/plug should be fixed, but it won't matter if it isn't. Even if the TB heater element isn't working that won't cause problems, especially in this country. It's possible you IAT is breaking down or your TPS is a little sensitive at low RPM, but they rarely go wrong.

 

In situations like this, it's just as easy to do complete one for one swaps, i.e. the whole TB or just the sensors (if you can get to them) and see - one thing at a time - what cures it. It's a simplistic and non-too-technical approach, but it works.

 

Sarty's advice: Look for cracks in tubes - check MAP tube - check and lubricate throttle linkage* - do the engine earth check I described in 'Sluggish Mi' topic (add earths as necessary) - swap TB complete.

 

*This is my new theory. Replacing the cable may fix this.

Edited March 5, 2010 by DrSarty

[kyepan 291]

I emplore you to give that whole area and all related connectors a good clean, wd40 and an old tooth brush, some old tshirts to wipe with.

 

Oil is a fairly good conductor because of it's carbon content... in days gone by dad was called by a neighbour who could not start his car, dad cleaned all the oil and s*it off the coil and plug leads... car started, neighbour was shocked as the car ran better than it had done for ages.

 

Then check your earthing points for corrosion (i must sound like a broken record) as poor earths will give erratic running especially at low revs where the alternator is not pumping so hard.

 

please don't take this as harsh, but poor cleanliness in the engine bay, especially around electrical components is asking for trouble.

[supersub14 1]

Surely what I typed wasn't that confusing?

 

Did you try the MAP tube test?

 

Your inlet hosing looks OK (if a little grimey) but have you found any splits?

It wasnt confusing im just a complete novice lol

 

Did the MAP tube test and there are no leaks and it is connected to the ECU.

 

Again cant see any splits on the inlet hose but i want to replace it as that could be why there is so much oil slpattered round the TB.

 

I emplore you to give that whole area and all related connectors a good clean, wd40 and an old tooth brush, some old tshirts to wipe with.

 

Then check your earthing points for corrosion.

 

please don't take this as harsh...

 

Gonna strip down the whole TB area and clean it up. I agree that there is too much oil pished out over it.

 

And the harsher the better lol

[welshpug 1,657]

splits in the inlet hose wouldn't cause any issues as it does not have an air flow meter.

 

splits on the Idle valve hose and any leaks engine side of the throttle body would though.

[supersub14 1]

Stripped everything down today and gave it a good clean with WD40. Noticed that the vertical bar (arrowed) was slack so tightened it up. Throttle pedal feeds bit more responsive now so im happy about that:

 

 

I also tested the TPS while it was off the car and it seems to be working fine too. Ill just post my findings incase anyone else has issues with theirs.

 

(I stole this image from the 205drivers.com home page but it illuastrates my point)

 

 

On my TPS the pins are numbered 3 - 2 - 1 whereas in the image above they are 3 - 18 - 2. Using my relevant pin numbers, i set my multimeter to resistance and found:

 

Valve closed :

1.01K across pins 3 + 1

2.40K across pins 3 + 2

 

Valve opened :

2.40K across pins 3 + 1

1.01K across pins 3 + 2

 

Resistance seemed to rise / fall in porportion to how far open the valve was.

 

To me this is working normally unless someone else tells me differently

 

I also did the earth test to different components on the engine (as stated by DRSARTY in the "Sluggish Mi" thread) and everything i tested read 0V so happy about that too!

 

Car felt better to drive but it might just have been in my head cos i spent so long cleaning lol

 

Im still aiming to swap sensors and TB when i get replacement parts to see if there is a difference.

 

Cheers for all the help lads!!