As mentioned in a previous post, it is common to uncover hidden problems that were not found during the test drive. And 2 of them are particularly annoying. In this post, I talked about the bouncing idle rev problem.
- Bouncing idle – The idle rev jumped up and down between 800 and 1200 after the engine reached the working temperature. I first spotted this issue at a time we stopped at the traffic light and waited for the green light
I asked the seller and the previous owner about the bouncing idle and was told that the symptom has been there for long and made no impact to the performance so that it can be ignored…..🤔 Since then I searched for answers from every Alfa forum I could found through Google. One by one from different sources, I found many probable causes and solutions. I had no luck by trying some of them right after if the solution is DIYable☹
Possible causes of bouncing idle
I listed those I found for your reference. I’d suggest diagnosing the cause with actions following the order from the top to the bottom if you unfortunately encounter the same problem and don’t have access to the Alfa diagnostic computer.
| No. | Cause | Solution |
|---|---|---|
| 1. | Not sychronised idle control and ECU | Conduct the ‘ignition key procedure” ECU reset. You can find the procedure from the following URL: https://www.alfaowner.com/threads/ecu-reset-its-a-miracle-cure.201163/ |
| 2. | Leaking intake tube between MAF & throttle | Use the “soap water” trick to check if the tube has cracks |
| 3. | Dirty throttle valve | Clean the throttle valve with carburretor cleaner |
| 4. | Faulty MAF | Borrow a unit from a healthy car and test if it is the cause. if yes, replace the unit |
| 5. | Broken idle control | ditto |
| 6. | Bad O2 sensor | ditto |
| 7. | Clogged fuel injector | Clean the injectors with off-the-shelf products. (If no improvement, it doesn’t mean the injectors are fine. It would be too bad for the cleaner to be effective) |
If none of the above solves the problem, you likely need help from a good Alfa mechanic. It is because you may need professional tools and knowledge to remove and test the components that DIY may not be possible.
In my case, none of them is the cause of the problem. Only six months after I bought the 156, the cause was found and fixed unintentionally.
Solution
Since I was thinking of keeping the babie for a while, I had the timing belt and the related components, such as water pump, tensioners replaced by a local Alfa specialist. When I got the car back, the mechanic told me that they believed the previous timing belt installation was misaligned from the correct position for one “tooth”. Since he was confident to his judgement, he installed and tested the new belt following his way disregarding the previous setting. He advised me if anything seems wrong, do let him know. It turned out nothing wrong and unexpectedly, the bouncing idle disappeared since the new timing belt has been installed.
Would the misaligned cam belt be the cause of the bouncing idle rpm? I think I found another cause of the problem other than those I found from the net.
Another problem uncovered
For another annoying problem – “Burnt out light bulbs inside the climate control unit” – I’ve written a post about how to fix it here: https://alfa156.club/?p=94
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