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Oct 04

Solutions to the Subaru BRZ and Scion FRS rough idle problem

With any new car there will be some growing pains. The Subaru BRZ and Scion FRS are no exception to the rule. It appears that some number, particularly of the first batch to be released, have an issue with rough idle. Immediately I figured it was an ECU issue as that would be the most common cause. Toyota agrees, but Subaru does not. Let’s take a look at the hows and whys of both companies arguments.

Rough idle is particularly an issue that often creeps up on first year cars. Usually it is how the fuel is mapped and a simple tune fixes the problem. GM cars, particularly four cylinders have had this issue quite a bit. Toyota thinks that something in the FRS’s ECU is causing the problem for it’s car. What happens when you start a car is a signal is sent out from the ECU to all the sensors to check that everything is working ok. This is called a handshake. According to Toyota the handshake in the FRS is getting interrupted by a faulty connection. It is certainly possible. So what they are doing is that if the car has less then 100 miles they are just reflashing the ECU. However if the car has over 100 miles the ECU is locked and a new ECU will be needed.


Subaru thinks the situation is a bit different with the BRZ. They do not believe the issue is mileage dependent and will just reflash the ECU at any mileage. What I suspect is that the Subaru dealers are doing a rewrite as opposed to a reflash. There is a difference between the two and the later completely erases and rewrites the entire ECU while the reflash simply just flashes the maps. It’s splitting hairs really but it’s clear Subaru is using a different strategy for their fix.

The problem however is that many BRZ/Subaru owners have reported that these solutions are not fixing the rough idle problem. In fact many dealerships have had to replace the camshaft bearing and cam gear to fix the problem. So if your BRZ/FRS is still acting up after the reflash you may consider taking those additional steps.

If the problems persist Subaru and Toyota will have to find another fix and it seems that the dealers are on the right track with the cam bearing and gears. We will keep you informed on what is going on with this issue.