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The headgasket on the car went and due to time issues I had it fixed a local mechanic.
When I went to collect the car he told me the car was hunting and that I should replace the Throttle Body.
With hunting I mean, when standing still at a traffic light the car idles very low. Just over the 500rpm mark. When in neutral it fluctuate between about 800 and 1100 rpms. When driving there is no issues. At low speeds the brakes are also very soft. But as soon as I start driving it gets normal again. Only happens with first start in the morning when driving out of the garage.
I removed the throttle body and replaced it with an decent secondhand one. The problem still persist. The old one after taking it out and stripping the black part it showed clear signs of the wires disintegrating. Does the new throttle body need to be programmed or learned?
I have checked the mass airflow sensor. No difference in the idling with it on or off. I presume it is still decent. It has a Bosch airflow meter.
I have opened the wiring harness on 2 spots. One being the wires going to the fuel injection. They seem to have been replaced by a previous owner. No sign of bad wires. (Pics below)
I have a suspicion this could be a vacuum problem? How would I go about checking that?
What else can I check before spending more money at mechanics that doesn't seem to be able to find the problem?
Hi rb za81, I hope this helps. The symptoms you've described, such as low idle, fluctuating RPMs, and soft brakes upon first startup in the morning, might indicate several potential issues with your Mercedes W202 C220:
Vacuum Leaks: Vacuum leaks can cause erratic idling and fluctuations in RPMs. Check for cracked, damaged, or disconnected vacuum hoses around the engine. Use a smoke test or a vacuum gauge to locate leaks.
Idle Air Control Valve (IACV): A malfunctioning or dirty IACV might lead to low idle and erratic idling behavior. Cleaning or replacing the IACV could resolve the issue.
Throttle Position Sensor (TPS): While you replaced the throttle body, a faulty TPS could still cause irregular idle. Test the TPS to ensure it's functioning correctly.
Mass Airflow Sensor (MAF): Even though you tested it, a dirty or failing MAF sensor could still cause idling issues. Cleaning or replacing the MAF might help.
Brake Booster or Vacuum Line: Soft brakes upon startup could indicate an issue with the brake booster or a vacuum leak in the brake booster vacuum line.
ECU Reset/Relearn: Sometimes, after replacing components like the throttle body, the ECU needs time to adapt and recalibrate. Performing an ECU reset or relearning procedure might help.
Checking for fault codes using a diagnostic scanner like the Youcanic scanner is crucial. It might reveal specific codes related to the issues you're experiencing. Additionally, it's recommended to perform a thorough visual inspection of the engine bay, paying close attention to hoses, connectors, and wiring harnesses for any signs of wear, damage, or leaks.
If the issue persists or if you're unsure about performing these diagnostic steps, consulting with a qualified mechanic or technician experienced with Mercedes vehicles would be advisable. They can conduct more in-depth diagnostics and perform specialized tests to pinpoint the exact cause of the problems you're encountering.
12-12-2023, 11:58 AM
