Rav4 D4D P1251 VSC TRC fault and turbo flat spot

October 14, 2019

Scenario

Driving up a steep hill accelerating hard in 2^nd gear and upon changing to 3^rd the car went into limp mode, power dropped off and car was only able to crawl in 1^st gear so had to pull over. I switched it off, had a quick search on the internet and one of the first things to check was the fuel filler cap. It was tight on as it should be but upon restarting the car it ran ok….ish. The VSC TRC light went off but the engine light stayed on.

Background

The car has been handed to me by my mother. She drives like a granny (because she is one) and the car probably only did 1 mile per day. She only had it for 6 months and acquired it purely due to it being a bargain from a family member. She first found the fault a few weeks ago. Her mechanic said to take the car for a thrash around, but her idea was a 10 mile jolly along the local main A-road (once) then back to her usual driving. The fault had returned because of her driving style, so we decided to swap cars as mine was a small petrol car but I did more long/fast journeys so perhaps it would be better with me. Anyway, as stated above, the fault happened on the second day I drove it, so here’s my story.

Solution

I am an engineer (albeit electrical) so I knew that the filler cap wasn’t the issue (although in some of the forums people said they have replaced it and the issue went away). The first thing I did was check the basics (oil level, coolant, tyre pressure). I then cleaned the EGR (https://www.youtube.com/watch?v=JND3ymzmCQM) with carb cleaner and cleaned the MAF sensor using Halfords electrical contact cleaner as it leaves no residue (https://www.youtube.com/watch?v=t3iJEA6kIvk).

I then took the car for a spin along an A-road where I could get up to the legal speed. You need to listen carefully to the car, so windows up, no stereo and minimal/no fans on. I was listening for the whistle of the turbo; so in 1^st and 2^nd it was fine up to and beyond 3000 rpm. Then whilst accelerating hard in 3^rd I noticed a flat spot at about 3100/3200 rpm. I drove through the flat spot, changed to 4^th and I felt it again at the same rpm.

I began to panic as I thought the turbo was duff and it wouldn’t be a cheap fix. I was fortunate enough to have an OBD fault code reader from years ago. I plugged it in and got the code P1251. That was all the info I got from the reader, but everything was pointing towards the turbo and pressure – so panic even more.

Before jumping to conclusions and stripping things to bits, I spent ages looking online for fixes. The forms said to check the connections of the hoses, so I traced them all and they were all connected, but one of the most interesting things I found was how the variable vanes on the turbo work. If you watch these videos (part 1 https://www.youtube.com/watch?v=cjtz8tmEaNE and part 2

I then did a search for turbo cleaner, and I was surprised to find there are loads of additives out there, so I started to have a look at the reviews. The one I thought was worth a try was Wynns turbo cleaner, so I drove to Halfords and £10 later I was ready to go. I then headed to the service station, put the Wynns in the tank and filled up with 40 litres of Shell V-Power diesel.

Now I had read that the Rav4 D4D was the “Golf GTI” of the SUV world, so now it was time to drive it like a GTI. I took the car for a long drive and exercised the turbo beyond the 3200 rpm mark. I repeated and repeated, slowing and accelerating and getting the car up to high speeds and high load on the motorway. By working the engine the turbo started to unstick and it would rev more easily beyond 3200 rpm.

Day 2 (my commute to work) I took the risk that the car wouldn’t go into limp mode and I drove getting the car nicely warmed up. When it had reached temperature I started to exercise the turbo revving it up to over 4000 rpm before changing. As it has been dark I couldn’t see what was coming out of the back, but I guess it was puffs of black smoke as the contaminants are being ridded from the engine and turbo (sorry environment, but I am trying to make it cleaner in the long run and prevent another component or indeed car being scrapped). After my day at work I started up, but this time the engine light had gone out. I checked the odometer since the decent fuel and Wynns and I have been thrashing about for 90 miles.

The car now revs freely, the fault lights are gone and it seems to be going fine. Of course there is the placebo effect and the sin of altering 3 things at once (the fuel, the Wynns and the driving style), but I had to fill up with fuel regardless, I was making the 90 mile journey regardless (albeit thrashing) and the Wynns was a £10 whim which had good reviews so why not try? So did it work? For me it seemed to, but I have found out a couple of things that you shoud note.

I will agree with others that the expensive fuel does seem better. Today I was speaking to someone who works for a well-known oil additive company, and they have said that Costco have some of the best diesel, so this evening I’ll be applying for one of their memberships as fortunately they have a filling station right near my work. The other thing is that after driving the Rav and giving it a good thrash, it does seem to be an SUV GTI, and you can happily drive around like you stole it.

I am aware not to labour the engine at low revs and high gears for the sake of ‘economy’ thus causing it to burn dirty repeat the issue again. If you drive them hard it will flex the turbo and keep everything clean. As for me I will continue to thrash it around as well as drive sensibly, and I’ll throw in a few more tubs of Wynns (once every 4^th fill I believe) until I feel happy that a good portion of the carbon deposits have been blasted away; well as best they can without an intrusive clean. Hope this helps : )