Lumpy idle but no problem at higher rpm

[Ezra-RS]

As the title says, I have a nasty lumpy idle on my 172 phase 2. It started doing this after the cambelt and dephaser were changed :S (The mechanic who did it also said it wasn't done properly the last time, with tipex markings and such..)

However, there's no problem at all in the higher rpm's. It drives and pulls fine then. Just until about 2.5k rpm it's bogging sometimes and stalls now and then when at standstill. (So I'm heel-toeing towards stoplights now :clown

I changed the plugs with new ones. I also ordered a set of leads. If it's not that I'm going for the coilpack.

​Anyway my question is: can I do anything to try to pinpoint the problem? Like unplugging the leads or injectors one by one? Or the lambda? Maybe other sensors to check?

 

[MicKPM]

​Anyway my question is: can I do anything to try to pinpoint the problem? Like unplugging the leads or injectors one by one? Or the lambda? Maybe other sensors to check?

Personally, and no offence to your mechanic, unless there's something obviously unplugged or not looking right on live data I'd start by checking the last thing done (timing) as by your own admission it wasn't doing it before.

 

[Ezra-RS]

That's also what I was thinking. But he does loads of RS's for the Dutch club and he's very high regarded for his skill and knowledge.

Anyway, how do you go about checking the timing?

 

[MicKPM]

Basically take the plugs out and rotate the engine to TDC on cylinders 1 & 4. Then insert tye crank pin and camshaft locking tool.

It should all slot in without any real drama.

 

[Ezra-RS]

Well I don't have the tools so I won't be doing it myself. My bet is that there's some sensor knackered because I can't imagine the mechanic fing this up honestly..

So what is there to test? And better yet, how to test it?

 

[Munson]

Take it back.

 

[MicKPM]

Take it back.

This... messing yourself will invalidate any warranty you have and if he's as reputable as you say he'll do all he can to make sure you are happy and that the car is right.

 

[Ezra-RS]

This... messing yourself will invalidate any warranty you have and if he's as reputable as you say he'll do all he can to make sure you are happy and that the car is right.

Yeah that'll be the quickest way I guess. It's just that I took the car because I needed it and it's a two hour drive. That's why I thought I'd check things myself first .

 

[m4tt274]

Check the idle control sensor. Mine seeks a little and thats the reason.
May just be a coincidence.

 

[Ezra-RS]

It's a phase 2 so it doesn't have one.

 

[Ezra-RS]

Could someone shed some light on the readings I took from the coilpack?

This is how I took the measurement: (So the coilpack is like standing in front of the car)

Coils:
3 4
2 1

Connector pins:
8
7
6
5

Here's what I got for the secondary resistance:

1-4 7.29 kohm
2-3 7.27 kohm

As it should, near similar. But in the manual it says 11 +- 1 kohm!?

Primary resistance of the pins: (Didn't know which ones I was supposed to take, so took them all)

5-6 1.3
5-7 0.8
5-8 0.8

8-7 0.3
8-6 0.9
6-7 0.8

Also spoke to the mechanic and he said I could come in whenever I wanted. It's just that I don't have the time to go until next weekend so until then I'm checking things myself.

 

[Dan@SJM]

The lumpy idle, could be down to it having the correct timing now. They always have a slightly lumpy idle, and in last experience tend to idle better when the timing is out.

 

[Ezra-RS]

Yes, but that surely doesn't mean it'll shake and sometimes stall, right?

 

[Dan@SJM]

Reading fail. I entirely missed that. If its that lumpy the timing is out. I skim read it, now I've read everything in it, I'd say timing is out.

 

[Ezra-RS]

Alright! That seems to be consensus then!

If that is the case, can it do any damage if I drive to the mechanic? (Mind it's a 2 hour drive)

 

[Dan@SJM]

Well providing its not slipping, it should be ok. I however accept no responsibility if it breaks down

 

[markhinton]

This is going to sound ludicrous, but have you called the mechanic who changed the cambelt? He might be able to offer his services by getting someone out to you. You will have just paid a fair amount to him and if he has a reputation to uphold surely won't be requiring you to drive your car out on a 2hr trip whilst it's in this condition?

 

[Ezra-RS]

I made an appointment for coming week. He said it can't be the timing because he double and triple checked after he saw it idling like that afterwards.

I then just took it because I needed the car again, couldn't really leave without it. Anyway, I'll post up whatever was wrong (if it's gonna be fixed )

 

[MicKPM]

That's why you shouldn't go all guns blazing stating he has ballsed it up. Simply ask him to investigate the issue as it wasn't there before the belt change.

It may be that something isn't plugged in... I've been guilty of this before. It may also be the timing has slipped for one reason or another but until it is properly looked at we can can only speculate and if this guy is as good as you say then you have to be fair and give him the oppertunity to firstly check it out and if it is his fault, to put it right.

 

[Ezra-RS]

Yes, you're right and that's exactly what I'll do. Everybody can make mistakes but he's handy enough so I guess he'll get it sorted.

 

[Ezra-RS]

Brought the car back and timing was checked together with working replacements for: MAP sensor, o2 sensor, throttle body, coil pack, tdc sensor.

Also checked (the new) plugs and leads, cleaned injectors and checked fittings of all hoses. Used new gaskets for the manifold.

All of which didn't result in a better running car. It also had the dephaser changed but can't possibly pose a problem because it doesn't do anything at idle.

It's proving to be a bit of a mystery!

 

[Ezra-RS]

Prepare to be amazed by what the problem was..

Some a@*hole before me thought it was a good idea to put some longer than standard bolts in the inlet manifold and didn't stop there because you can see the marks of where they were touching and boring into the alloy below.
It also came off with a liquid gasket but the mechanic I went to just put on a standard gasket afterwards. This left a small gap and so it was ever so slightly sucking in air, causing all this. :quiet:

In every case of finding a problem, it's in the last place you look. Because after fixing the problem you don't look any further. In this situation however it really was about the last place you could look for it.

​Anyway, I'm happy it's sorted now

 

[-J-]

Glad it's sorted