ANOTHER lumpy 172

[Sunday_Driver]

Hi all!

Hoping for some suggestions on what to check out to narrow down my idle issue.

I recently picked up a P2 172 that’s done ~180k kms.

Since I’ve owned it it’s had a pretty rough idle, which I’ve heard is common on these cars but recently it’s gotten worse to the point where it stalls easily while reversing.

The car runs perfectly once it’s moving, but during idle it sounds like a boat. It doesn’t hunt, the needle stays steady, it won’t die while stopped and starts with no issues.

Previous to me owning the car, the belt & dephaser were replaced less than 10k kms ago, and I’ve been assured by the mechanic that did it that the timing is correct, was done by some French specialists here in SA. At the same time the coil pack, leads & plugs were inspected, but just the plugs replaced.

I’ve replaced the injectors because they’d never been replaced and we’re looking a little tired, this improved the way the car drives, but not the idle.

I have an RS tuner so once I’m home from work I’ll get some live data so that hopefully someone here can better diagnose.

What live information is needed to better identify an idle issue?

Any help you can offer would be hugely appreciated

So far I have;

• Lambda Sensor Voltage
• MAP Sensor reading
  
  Once I’m home this evening I’ll post the results and like I said, hopefully someone more knowledgeable can help me diagnose. Cheers!

 

[Brigsy]

Check map sensor readings are around 400mbar on idle, that will give you an idea if cam timing is correct. Also should read around 1000mbar atomspheric pressure with ignition on engine not running.

Lambda voltage on pre cat sensor should rise and fall fast over 0-1v scale from memory as narrowband.

Id do a compression check first to make sure engine is healthy and check no vac leaks on plenum, ht leads are routed correctly and not arching out.

 

[Sunday_Driver]

I don’t have a tool to do a comp test unfortunately, will get one this weekend.

Thankfully the leads looked okay, couldn’t hear any leaks on the plenum, nothing obvious either.

• Lambda mV jumped up and down from ~300~700.
• Ignition on, atmospheric pressure was 1028mbar.
• At idle, MAP was reading ~484 > ~513

 

[Brigsy]

Doesnt sound too bad. As above compression test to see if any internal issues with the engine. If all good just save all parameters on Rstuner and check air temp, coolant temp sensors for any erratic readings.

If you have access to can clip, assuming all sensors reading ok, id clean throttle body and reset fuelling adaptives and throttle settings and let the ecu relearn, might cure it.

 

[Sunday_Driver]

Hey @Brigsy sorry to revive a bit of a dead thread here but im still having issues almost a year later.

In a previous comment you said "Check map sensor readings are around 400mbar on idle, that will give you an idea if cam timing is correct." can you elaborate on how the MAP sensor reading would indicate if the cam timing has been done incorrectly?

Im taking it back to the shop again today and need some justification for why they should check the timing. Theyre adament that if the timing was out the car wouldnt run and would be slapping valves, but at this point everything else has been checked.

 

[SharpyClio]

Hey @Brigsy sorry to revive a bit of a dead thread here but im still having issues almost a year later.

In a previous comment you said "Check map sensor readings are around 400mbar on idle, that will give you an idea if cam timing is correct." can you elaborate on how the MAP sensor reading would indicate if the cam timing has been done incorrectly?

Im taking it back to the shop again today and need some justification for why they should check the timing. Theyre adament that if the timing was out the car wouldnt run and would be slapping valves, but at this point everything else has been checked.

The timing on mine was out when I got it, ran okay when moving but was lumpy on idle and prone to bogging down / almost stalling. It was one tooth out. If the timing is a tooth or two out then it wont result it a snapped valves but bad running. On the basis that they are saying that I would go to a different garage.

 

[Brigsy]

Map sensor vac readings on idle are usually off if cam timing is out. Id personally get the timing checked by a specialist or somebody who knows what they are doing with an f4r. Looking at the map readings above they are quite high, im sure mine was around 400mbar on idle.

 

[Sunday_Driver]

Yeah the mechanics noted themselves that the MAP was reading high at idle.

Unfortunately without taking it to a Renault dealership ($$$) they are the only French experts in SA. I’ve dropped the car back off to them today and told them to actually go back in and check the timing, they’ve agreed to do it at no cost to me so they’re trying to help at least.

Appreciate both you guys’ advice, it’s nice knowing there’s always a bunch of forum guys willing to lend some guidance.

 

[Sunday_Driver]

Got a call from the shop late yesterday and have been advised that the timing was out by 1/2 a tooth. They went back in timed it all up properly, it ran fine initially then they took it out for a drive & got it to full operating temp and when they came back to the shop the rough idle had returned.

This doesn't make sense to me, have you guys got any other suggestions for what would cause a high MAP reading and rough idle?
I'm at the point where I think I'm just going to sell it, its cost me more in maintenance in the past 12 months than the cost to buy it 🥲

Video of it running:

 

[Louis]

Got a call from the shop late yesterday and have been advised that the timing was out by 1/2 a tooth. They went back in timed it all up properly, it ran fine initially then they took it out for a drive & got it to full operating temp and when they came back to the shop the rough idle had returned.

This doesn't make sense to me, have you guys got any other suggestions for what would cause a high MAP reading and rough idle?
I'm at the point where I think I'm just going to sell it, its cost me more in maintenance in the past 12 months than the cost to buy it 🥲

Video of it running:

Sounds normal tbh.

I'd do leads, coil pack, spark plugs, injectors and then just live with it.

Is it flashing EML at idle?

 

[hopgop1]

Were proper genuine magnetti marelli injectors put in it when you changed them? Definitely sounds rougher than my 182 at idle, but not miles off.
Is the MAP reading improved at all since they re-did the timing?

 

[Sunday_Driver]

Were proper genuine magnetti marelli injectors put in it when you changed them? Definitely sounds rougher than my 182 at idle, but not miles off.
Is the MAP reading improved at all since they re-did the timing?

Yeah genuine MMs were used, bought from Ktec.
MAP sensor reading has not improved, still sitting around the 500 mark. they pulled all the timing kit off and started from scratch and confirmed that they put everything back together using all the correct tools and it still has that same lump and idles like poop.

Could a worn dephaser do any of this? I wouldn't have thought so but they said that was the only thing they could think of, but after visually inspecting the current dephaser they said it was a long shot and didn't recommend swapping it as they cant guarantee it would fix it.