Fluctuating / bad idle

[AndyW]

Hello everybody. I am new in this forum. My name is Andy and I come from Germany. Since 2 years I am proud to be the owner of a MG ZT 260.
Now i have a little problem.
I took him out of the garage. He started normally first. When rolling down the hill I had 2 light hits, like backfire, in the exhaust. Then he rumbled as he accelerated. The engine was running totally rough at idle. The rpm fluctuated between 300 and 500 rpm until it went out completely. In terms of exhaust gases, it smells extremely like gasoline. As if he's not burning properly. After restarting, the engine speed did not exceed 2500 rpm, moreover it started to wobble and did not accelerate.
I brought him to my trusted Garage. Fault code read out with T4 tester: P0113
So far we have swapped the MAF sensor, IAC valve and cleaned the throttle budddy.
After swapping these parts, it hast become a little better but did not solve the problem yet.
Now he starts normaly and holds the idle rpm correctly. But after few minutes the idle starts to fluctuate again and a strange noise comes from the vicinity of the IAC valve. A short time later the idle is back to normal. Then the problem repeats.
Big question mark!
Maybe someone has another idea what to do?

[SCP440]

P0113 is high inlet temp. If you have a bad idle and are getting this code I wonder if the EGR is stuck open or partially open?

Try blanking it off to see if the engine runs better. Just make up a metal plate and undo the two bolts that link it to inlet manifold.

Steve

[colintf]

Hi Andy and welcome.
hope it's sorted soon. Whereabouts in Germany? :)

[AndyW]

Thanks for the Tip Steve. We will have a look on the egr valve. I will give a feedback later.
@ colintf : come from Hagen in Germany.

[colintf]

Thanks for the Tip Steve. We will have a look on the egr valve. I will give a feedback later.
@ colintf : come from Hagen in Germany.

That might help others with local knowledge help you Andy :)

[AndyW]

Update: egr valve works perfect. But the problem ist still there.☹️

[Nich]

Update: egr valve works perfect. But the problem ist still there.☹️

Have you checked to make sure the fuel pump has not separated, it's under the rear seat squab on the right of the car looking from the front.

Nich.

[SCP440]

If you can plug a code reader in with live data you should be able see what is going on. Fuel pressure, lambda outputs, IAC activity, EGR amongst others depending on the reader. Reading the information is very important, for example a lean mixture can be an air leak, a bad injector or low fuel pressure, miss firing plug or even a fault lambda sensor. A misfire will allow unburnt oxygen into the exhaust and the lambda will read this as a rich mixture so lean the mixture off.

The fuel pressure on these engines does fluctuate as the pump speed controls the pressure rather than a pressure regulator. Low fuel pressure as Nich has said can be caused by the pump separating but also by a faulty sensor on the fuel rail or even the fuel pump controller it self.

If the code is cleared does the same fault code come back?

Steve

[AndyW]

So new update.
When the codes cleard, they did mit come back. Today i worked with the mechanic at the car. When we start it, there was the creepy noise again. When we took of the hose from the IAC Valve, we mentioned, that there sucked Air in but also Air comes out. It's like bubbling. Hard to describe.
At first we thought that the catalyst were clogged. So we sepperated them from the exhaust mainfold. Same Problem.
So we put everything together again.
now we suspect a defective intake valve, because when the engine gets warmer, the noise comes directly.
Tomorrow my mechanic want to unscrew the valve cover and do a pressure test.

[David]

The padded hose from the PCV valve on the left hand cam cover over to the throttle body plenum, maybe? Often the rubber elbows at each end can leak or become soft and collapse. The PCV valve itself should be replaced every 80k Miles.

I can confirm the Motorcraft part numbers are:
PCV valve: EV-261 (2C5Z-6A666-AA)
Hose to Throttle-body: KCV-240 (2L2Z-6A664-FA)

Unsure of MGR numbers, if thee are any.

David

[re-tread]

If you separated the catalyst convertors from the manifold and still had the problem then it may be one of the O2 sensors either side of the cats. I had a similar problem, which continued to get worse until it changed to a missfire, which in turn destroyed one of the cats. I replaced the cats and the failed O2 sensor and all was fine and has been ever since.

[AndyW]

@ David: the hose from the IAC valve Plenum Body which goes goes back into the air intake hose after the MAF sensor.
@ Dave: when the o2 sensors are bad, there should not be an Error Code?

[SCP440]

Not always, a small air leak and a lambda that is still giving an out put but wrong might not be enough to put the light on. This is why it is useful to look at live data.

An air leak will obviously lean off the mixture and this should show up as the compensation should be quite high trying to get it back to where it should be. Look at the swing on all of the lambdas, they should all have the same amount of swing. You can move them from side to side if you want to test them.

Steve

[David]

@ David: the hose from the IAC valve Plenum Body which goes goes back into the air intake hose after the MAF sensor?
Not that hose, the other one, rearwards of it and lower, the positive crankcase ventilation valve and hose. It goes from the top left cam cover (the valve itself) just underneath the air trunking, to the plenum right of the tail of the Mustang on the throttle plenum plaque (so between the IAC and the EGR).

Look at the pictures. Here is the hose on eBay at the moment:
https://www.ebay.co.uk/itm/333612093681

... and the PCV valve itself, (a service replacement item at 80k say Ford, 90k say MGR):
https://www.ebay.co.uk/itm/MG-ZT-260-V8-Rover-75-V8-PCV-Later-Cars-with-heating-element-Genuine-Ford/193425163719?hash=item2d0909c5c7:g:CMwAAOSwKNpel4p 6

Available cheaper from the States of course, under the numbers I quoted in the earlier post.
When mine went bad, I did indeed get lean-mixture error codes after a while, but not straight away.

David

[WNJ516]

When you take the hose from the main air intake pipe to the IAC valve OFF the engine will stop running. Is this the case, the live data for this valve at idle should be around 50% and about .5 amp from the live data on my car.

[AndyW]

When we took the hose off, the engine did not stop running.

The hose from the crankcase ventilation valve is okay, also the valve itself.

[WNJ516]

Has the throttle idle screw been adjusted,ie the engine is having too much air at idle,giving the wrong idle speed which the IAC valve is now trying to control, via the ECU.
What is the voltage out of the throttle position sensor @ ign on, engine OFF, should be below 1volt. i.e. .95V
My engine has always stopped when taking the pipe off the IAC, you need to have the live data to check what this valve is doing.

[AndyW]

Hello all. I think we have found the Problem. My mechanic did a pressure test at the inlet and outlet valve. Everything was fine. Then he looked at the timingchains. One timing chain is loose. The other is tight. it looks like she's skipped a tooth.
Now i order new complete timing Set.

[David]

Hello all. I think we have found the Problem. My mechanic did a pressure test at the inlet and outlet valve. Everything was fine. Then he looked at the timingchains. One timing chain is loose. The other is tight. it looks like she's skipped a tooth.
Now i order new complete timing Set.

You might like to read this old thread. This may have contributed to/explained the death of the engine in #347?
https://www.two-sixties.co.uk/mgoc260/html/f0rum/showthread.php?10951-timing-chain-tension

P.S. If you do replace the chains, chain guides and tensioners, I would be interested in knowing if it was possible to do it with the engine in-situ. Mine is passed its scheduled change date.

David

[SCP440]

P.S. If you do replace the chains, chain guides and tensioners, I would be interested in knowing if it was possible to do it with the engine in-situ. Mine is passed its scheduled change date.

David

It must be possible even if the radiator needs to come out. There are several videos on You Tube showing it being done in Explorers and the like. My guess the problem might be the cam covers in our cars as they look quite tight, a trick I do on the Jensen is to undo one engine mount on one side and put a jack under the sump to tilt the engine a few degrees, this gives enough room to get some parts off.

What is the scheduled change date/mileage on these engines?

On a positive not a mate recently had the timing chains done on his Audi S6, the final bill was just over £5k and less than £1k of that was parts. Apparently if he had left it any longer the engine would have been scrap.

Steve

[ColinE]

Hello all. I think we have found the Problem. My mechanic did a pressure test at the inlet and outlet valve. Everything was fine. Then he looked at the timingchains. One timing chain is loose. The other is tight. it looks like she's skipped a tooth.
Now i order new complete timing Set.

Andy - the timing chain guides are NLA but I have several of both sides (LGJ000090 & LGJ000100) in stock if you need them £40 for the pair posted, just let me know

13019

[David]

... What is the scheduled change date/mileage on these engines? ...

Steve
Timing chains, tensioners, sprockets and guides is 150,000 miles according to Ford. MGR play the 'three-monkeys' and don't mention it. I assume back in 2004 they assumed that neither they, MGR, or any ZT260/R75V8 would survive long enough to find out that it should have been done !

David

[David]

Andy - the timing chain tensioners are NLA but I have several of both sides (LGJ000090 & LGJ000100) in stock if you need them £40 for the pair posted, just let me know

13019

Aren't those guides, Colin? Looks like there are two fixed guides, two pivoting guides and two tensioners. Example here:
https://www.ebay.com/itm/Timing-Chain-Kit-for-99-00-Ford-Mustang-4-6L-V8-SOHC-ROMEO-Oil-Pump-Water-Pump-/253673710345
... (example only; that particular one is for a Mustang 2V up to 2000; later ones have a different lower crankshaft sprocket, I believe. Take care!)

Lots of good timing-chain "how-to" videos on Youtube and this Ford instruction sheet: https://performanceparts.ford.com/download/instructionsheets/FORDINSTSHTCM-6004-462V.DOC.PDF

David

[ColinE]

Sorry more haste less speed, yes guides - post amended

[AndyW]

Thanks all for the help and usefull information, especially the Ford instruction cheet.
I orderd the timing Kit on Saturday from rockauto.com (USA).
When everything is done i give a new Update.

[AndyW]

So new Update. Everything rebuild. Car starts fine and doesn't Go out. The only Problem now is the idle. Idle now fluctuates between 500 to 1000 rpm.

[David]

So new Update. Everything rebuild. Car starts fine and doesn't Go out. The only Problem now is the idle. Idle now fluctuates between 500 to 1000 rpm.
Have you thoroughly cleaned the idle air control (IAC) valve? Sometimes a sticky throttle postion sensor (TPS) can cause that too, I hear.

David

[AndyW]

Now we put in the old iac valve. Fluctuating from 450 to 800 rpm. We did a test Drive. Accelerate ist verry good Till 3000rpm, then Acceleration breaks off and slowly takes on gas. We think there could be only two things now which are not working right. The fuel pump and or the fuel Filter.
No error Codes

[David]

Now we put in the old iac valve. Fluctuating from 450 to 800 rpm. We did a test Drive. Accelerate ist verry good Till 3000rpm, then Acceleration breaks off and slowly takes on gas. We think there could be only two things now which are not working right. The fuel pump and or the fuel Filter.
No error Codes
That sounds logical. Do you have the part number(s) of the timing chain kit or parts from RockAuto still? It would be good to know for other members who need to do the job (like me!). I assume they all fitted OK?

David

[AndyW]

1302613027
These are the parts i bought
Everything fits perfect

[David]

1302613027
These are the parts i bought
Everything fits perfect
Thanks, Andy. I'll put them all into a list and put them up into the INDEX for future use.

David

[SCP440]

You can monitor the fuel pressure to see what is happening with a code reader that does live information. There is a fuel pressure sensor on the fuel rail and the controller is in the boot. The speed of the fuel pump regulates the pressure with pulse width modulation.

Steve