CAR CLINIC | How YouTube helped fix a rev-happy Corolla

Peter, a retired guy, lives down the road from me. He shares my interest in cars, and machinery in general. Whenever we happen to meet in the street, the conversation turns to cars very quickly. This was again the case a few days ago when he told me wistfully that he had sold his car and that they now relied on his wife's little three-cylinder runabout to take them where they had to go. I was surprised to hear this. Peter had a 2007 Toyota Corolla 1.6 A/T, which was his pride and joy. It must have been a hard decision to part with it. Did the car give him problems?

It transpired that the Corolla had developed a habit of the revs going sky-high immediately upon start-up then staying there for a while before dropping. This will (and should) scare the daylights out of any owner who empathises with his car’s engine. We know the inertial forces imposed on the conrods when an engine revs like that under no-load conditions are horrific. In fact, on some modern cars the ECU will simply not allow high revs with the gearbox in neutral.

At this point, Peter was faced with a dilemma. Clearly, the Corolla had to be fixed, but he didn't have the money to pay a workshop to do it. This is where he decided to do a heroic thing for someone in his position: he will fix the car himself.

Bereft of money and knowledgeable friends, Peter turned to the internet, the great saviour of inexperienced DIYers in modern times. Prof Google revealed that excessively high idling speed at start-up on a petrol engine can be caused by a dirty throttle body.

Having never had to fiddle with a throttle body, Peter decided this would be a good starting point. Intensive scrutiny of various YouTube videos showing how to locate, remove and clean a throttle body convinced Peter he can do this. So he got his lead light out, rolled up his sleeves and started on the engine. The throttle body is located between the air cleaner and the inlet manifold on an engine.

On older engines, such as on Peter’s Corolla, there is a spring-tensioned drum attached to its side around which the accelerator cable is wrapped. When the accelerator pedal is depressed, the cable rotates the drum to open the butterfly valve. Various coolant hoses and sensors are also attached to the throttle body.

Following the beautifully clear instructions in the videos, Peter removed all the attachments on the throttle body, with copious use of stickers to record what goes where on reassembly. He could then take the throttle body out of the engine compartment. Using carb cleaner from a spray can, together with rags and ear buds or pipe cleaners, he cleaned the butterfly valve and the surrounding air horn thoroughly of carbon and lacquer deposits. 

Then it was time to replace the squeaky clean throttle body. With breathless anticipation the engine was started. Instantly the revs shot up to a screaming pitch. It was all in vain.

The spouse was kind enough to realise that silence is golden, but a stony silence sometimes speaks volumes. This is where true grit is born of tenacity and dogged persistence. Peter went back to the drawing board, or in his case the internet. Now he scanned the viewers' comments after each video. These are often a valuable resource when you are baffled.

And there he picked up a comment from a viewer who said: “Don't forget to also clean the Idle Air Control (IAC) unit attached to the bottom of the throttle body, especially the little rotating cylinder on the spindle.” Indeed, that was something Peter hadn't done. Once more everything was dismantled, and this time the IAC unit was given the full cleaning treatment. Again the throttle body was assembled and refitted, with hands now showing the scars of battle. (There is never enough space in an engine bay!)

With bated breath the ignition key was turned to starting position. Miraculously the engine almost instantly settled into a restful, 850 rpm idle. Mission completed. I listened to Peter's story in awe and realised how much it illustrated about DIY in 2023. The amazing value of the internet, the enduring role of desperation as a catalyst to bring out the heroics of which every car owner is capable, the necessity to absorb the setbacks (which there will be) and simply dig deeper.

Sadly, Peter had to sell the Corolla on which he had worked so hard, but at least he could find a buyer, who was no doubt impressed by the instant starting and steady idling of the engine.