Stuttering through gears up to 30mph issues

[Ianianian]

We have a 56 plate rx400 automatic petrol, with 135,000 miles and fully serviced.

In the last week there has been a stuttering of the engine when going up through the gears. Once at 40mph or so it seems better but is worse when you slow down for a roundabout and then speed up again. It feels like something is catching or there is a lack of power in the low gears and the car judders a little as it speeds up.

Could it be the gearbox or is there something else that may be causing this?

We recently had new tyres fitted and had the tracking done so I wonder if this is anything to do with it?

Any help appreciated.

[rich1068]

Plugs? Coil packs? Have you got a code reader? Plugs and coil packs are often ignored on the 400h because the back 3 are an arse to get to.

[Delphius1]

Do you have any abs or vsc warning lights on the dash?

Loss of power at slow speed especially when cornering tends to suggest a possibly traction control or stability control issue. The safety modules see an issue and cut the ignition, which can feel like a misfire, which to all intents and purposes that's what it is. It's just the modules cutting the spark.

Unfortunately on a complex car like the RX, the only real way of knowing what is going on is to hook it up to a diagnostic unit, preferably a PC running Techstream.

That way you can see what if any error codes are in the various modules.

The tyres may be an issue: what tyres did you fit and did you fit 4 identical tyres?

[Ianianian]

Thanks.

Rich1068 I don't have a code reader, do you mean diagnostic unit? 

Delphius, I have no warning lights at all showing. Can I get this diagnostics done at most garages? I think that is what I need to do.

I am not sure what the tyres were but we had a flat last week so I fitted the spare, which is being replaced this morning.

We are in France and the car is left hand drive. Trying to think if the issue happened before I fitted the spare? Could this be anything?

Thanks.

[jumpingjehovahs]

Could it be a blocked EGR Valve? This could cause the hesitation felt and as it gets worse could throw up a Check Engine Light?


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[Ianianian]

Thanks. Re the EGR valve, would I have this in a petrol engine?

I was going to say before that it feels like when I had a diesel car before and the exhaust was dirty and I needed to hit the gas while holding the clutch to try and blow out the balck smoke. It felt then like low power or stuttering when clicked, the same as I get now.

 

[Delphius1]

1 hour ago, Ianianian said:

Thanks.

Rich1068 I don't have a code reader, do you mean diagnostic unit? 

Delphius, I have no warning lights at all showing. Can I get this diagnostics done at most garages? I think that is what I need to do.

I am not sure what the tyres were but we had a flat last week so I fitted the spare, which is being replaced this morning.

We are in France and the car is left hand drive. Trying to think if the issue happened before I fitted the spare? Could this be anything?

Thanks.

Hi,

If the spare is a few mm different diameter than the other tyres, then yes, it could confuse the traction control system and cause it to engage. The problem is the system sees a wheel rolling at a different speed and assumes it's slipping, so the traction control reduces power to stop the slip. At higher speeds the difference between rotation speeds is a smaller fraction, so the traction control doesn't get involved.

A friend had a BMW with a faulty ABS sensor that caused a similar problem, misfire at slow speeds which went away above 40mph. I stuck an OBD scanner in the port, found the duff ABS sensor and once it was replaced he was good to go.  I had a job convincing him the car was working normally, based on the duff information the sensor was giving it. He was convinced the car had a misfire and was going to replace all the plugs and ignition coils.

These safety systems are great when the car is perfect, but they can quite easily be thrown out by faulty sensors or even something as simple as a mismatched tyre. You really should replace all 4 tyres on the car at the same time and rotate them around the car at intervals, because uneven tyre wear can cause issues not only with TC ABS and VSC systems, but also the AWD system. Luckily on the 400h there's no direct connection tween the front and the rear axles like the RX300.

OBD scanners are essential kit on modern cars. Most garages should have a professional scanner that will give you any fault codes. But they will charge to do it.

 

[Ianianian]

Thanks for all the replies.

I think it may have been the spare tyre being different to the other three that cocked up the timing.

I wouldn't say it is 100% better but it is a good 85% better with no drag or stuttering at all the vasy majority of times, so whislt I will note this to the garage on the next service, I hope we may be okay now.

Thanks again.

[Stupot]

On 2/5/2020 at 11:17 AM, Delphius1 said:

These safety systems are great when the car is perfect, but they can quite easily be thrown out by faulty sensors or even something as simple as a mismatched tyre. You really should replace all 4 tyres on the car at the same time and rotate them around the car at intervals, because uneven tyre wear can cause issues not only with TC ABS and VSC systems, but also the AWD system. Luckily on the 400h there's no direct connection tween the front and the rear axles like the RX300.

My RX300 has a 'new tyres' button that I stumbled across somewhere in the menus of the sat nav screen that I presumed does something/calibration but I don't know exactly what? I did press it recently after having two new front tyres. I have a part worn set of tyres on the back that so far has not caused any problems.

[Ianianian]

Stupot, what happened when you pushed the button? 

[Stupot]

1 hour ago, Ianianian said:

Stupot, what happened when you pushed the button? 

Nothing that I noticed! Was parked at the time and then ignition switched off, so perhaps needs activating just before driving. 

[ColinBarber]

4 hours ago, Stupot said:

My RX300 has a 'new tyres' button that I stumbled across somewhere in the menus of the sat nav screen that I presumed does something/calibration but I don't know exactly what? I did press it recently after having two new front tyres. I have a part worn set of tyres on the back that so far has not caused any problems.

All that is for is to allow the Nav system to calibrate the wheel diameter so when you lose GPS signal it still accurately tracks you on the road. It has no connection to the vehicle engine/transmission/drivetrain.

[Stupot]

13 hours ago, ColinBarber said:

All that is for is to allow the Nav system to calibrate the wheel diameter so when you lose GPS signal it still accurately tracks you on the road. It has no connection to the vehicle engine/transmission/drivetrain.

Thanks Colin. I doubted it would do much seeing as it was a feature available to owners rather than only dealer/mechanic.