Mi16 Cannot Idle Below 1200

[daveyboyblack 1]

Evening all,

 

Apologies for the slightly boring topic. I've done a search and come up with a few ideas so just want to check whether there's anything i'm missing before I start buying some new parts.

 

My mi16 (std running 2-row ecu) just won't idle below 1200 so has failed the mot (twice now and counting!).

I've changed the ecu temp sender, afm, idle valve and spark plugs. If I manually squeeze the idle valve pipe to try to get it down lower then it seems to just stutter and try to stall so it seems it's just not happy to run any lower.

 

Is it just the crank sensor, coil and ignition amp that are left that control the idle? Does the crank sensor actually have any effect?

 

Is there anything else that could be feeding into the ecu which would force it to try to idle high?

 

Apart from the idle speed itself, there is a slight misfire, however it revs freely to the redline.

 

Cheers

Dave

[Alan_M 66 1 Cars]

Is the TPS setup and working properly?

[Anthony 1,003]

Sure it's not the throttle body causing problems and not closing fully because of wear? They're well known for it unfortuntately, although if you're lucky, some of the early throttle bodies have an idle speed screw on them that might help being it down somewhat - certainly did on a friend of mine's car that had a similar issue.

 

That said though, a 1200rpm idle shouldn't fail an MOT on a pre-CAT car as far as I'm aware? Unless you're saying that the emissions are high as well.

[Alan_M 66 1 Cars]

Sure it's not the throttle body causing problems and not closing fully because of wear? They're well known for it unfortuntately, although if you're lucky, some of the early throttle bodies have an idle speed screw on them that might help being it down somewhat - certainly did on a friend of mine's car that had a similar issue.

 

That said though, a 1200rpm idle shouldn't fail an MOT on a pre-CAT car as far as I'm aware? Unless you're saying that the emissions are high as well.

 

Anthony's right. I had this on mine too and was a nightmare to track down. Hence why I'm running a GTi6 inlet & TB, car runs spot on.

 

Check spindles for play on the TB.

[daveyboyblack 1]

Cheers for the quick replies. Going to sound like a stupid question, is there always a tps present?

 

I believe the throttle body isn't original (told it was from a golf) and cannot see any wiring at all (maybe I need to take it off completely and have a closer look). There is no extra idle speed screw on it though.

 

Also, I would have throught that squeezing the idle valve inlet pipe would have the same general effect in reducing the amount of air going in, but it seems like the engine doesn't like that.

 

What exactly would I be looking for to find the tps?

 

It's failed the mot twice (not just on this issue) but on the second occasion i did query it and they had a large list of all cars/idle speeds. The original 405 mi16 was 875+-50 and the 205 Gti 900+-50. The garage have said that if I can get it down to somewhere around 1000 then that's reasonable and they would let it through.

Or is this just a case of 2 different mot testers being equally strict (certainly the second one today failed it on loads that wasn't even on the first advisories

[Alan_M 66 1 Cars]

Should be, it's a little black box on the back of the throttle body. Should be 3 pins on it, centre and one outer pin is for idle, centre and other outer are for throttle position.

[Anthony 1,003]

If there's no TPS present, the ECU won't get a "throttle closed" signal to use the ICV properly.

[daveyboyblack 1]

Cheers guys, looks like i'm best pulling the intake side apart to take a look before I start changing coils etc. Glad i'm not at work tomorrow as the MOT (or lack of it) has got me in the mood to get the car sorted!

[Alan_M 66 1 Cars]

Try and find the CapsDemo program on here. Basically explains how the management works, and aids fault finding greatly.

[pug_ham 245 3 Cars]

Try and find the CapsDemo program on here. Basically explains how the management works, and aids fault finding greatly.

here

 

 

Graham.

[Miles 331 1 Cars]

You are allowed a higher Idle speed on older car's so I would say 1200 is OK, you could always adjust you rev counter if there not using the HT lead sensor on it.

[daveyboyblack 1]

Quick update after a bit of work today. I took the throttle body off and gave it all a good clean up. There is definitely no idle adjustment on the body itself. Pulled off all the HT leads and connectors etc and the car is now at the stage whereby manually squeezing the idle valve intake pipe will allow the car to idle down at around 900rpm. Squeeze it fully and the engine dies.

 

As soon as you release the pipe, the idle goes back up to 1200. Great I thought, just put a bung in the intake pipe and that'll sort it. Well, it does kind of work, except that although it will idle lower, if you blip the throttle then as the revs drop back down, there's not enough range in the idle pipe loop to catch the idle back, so the engine dies.

 

I found the TPS, and tested the 3 connectors. Using 1 and 2, then the resistance varies on thottle openings. Using pins 2 and 3, there was no resistance until the throttle switch is opened, and immediately there's a load of resistance. So although i'm not sure of the values, it looks like the switch itself is working.

 

If you unplug the idle valve completely, then the engine dies immediately, so I had ruled out a leak in the inlet manifold/gasket.... maybe this was premature and that this could still be the issue?

 

It just seems that the ECU wants to put the idle high, and is pushing the idle valve open too much. Having changed the temp sensor, and now checked the tps, then i'm not sure where to go with it!

 

Oh, and unfortunately I can't get that CapsDemo program to run with Windows 7. I'll see if I can take a look at work next week. Thanks for the link though as unfortunately I always seems to need a hand with this kind of stuff!

[Miles 331 1 Cars]

Whats the part number on the TPS? worth checking as it maybe a VW one?

[boombang 2]

I had a Golf throttle body with Golf TPS as Miles is asking above.

 

Was wired the other way round to Peugeot.

[pug_ham 245 3 Cars]

I found the TPS, and tested the 3 connectors. Using 1 and 2, then the resistance varies on thottle openings. Using pins 2 and 3, there was no resistance until the throttle switch is opened, and immediately there's a load of resistance. So although i'm not sure of the values, it looks like the switch itself is working.

 

On the normal TPS you should have no resistance on pins 1 & 2 at idle / closed throttle, infinite resistance with the butterfly open on part throttle & then another switch closing it at WOT giving zero resistance again between pins 2 & 3.

 

Graham.

[daveyboyblack 1]

Quick update after a succesful day! Here's the unit:

 

 

Managed to trace the issue to the connector that comes off the TPS to the loom. The connection for pin 2 looked ok, but as you push the connector onto the tps, it was forcing the female connector out, so pin 2 effectively was never connecting properly. A few mins spent fiddling with the connections.... and hey presto idle is now nice and steady at an indicated 950rpm!!

 

Not sure if the pins are working exactly how Graham describes above still. Pins 1-3 being left to right from the image do seem to be related to:

1&2 - Zero on closed throttle, increasing as throttle is opened. On half throttle or more, it seems to be infinite.

2&3 - Controlled by the throttle switch. On closed throttle, the switch is depressed and resistance is zero. As soon as pin is lifted (throttle open), then this gives infinite resistance.

 

Either way, it appears to be working now so thanks for the help all!

 

Cheers

Dave

[Miles 331 1 Cars]

Thats just a std 405 TB

[daveyboyblack 1]

Thats just a std 405 TB

 

Just had a look on the article on the main site.. and so it is!! Cheers for the pointer!