Floating idle RPM — throttle position sensor

Symptoms: idle RPM fluctuates between roughly 1600–4000, and the engine revs up uncontrollably even with the brake pedal held down ^{1 23}. This happened on a pre-facelift automatic-transmission car right after starting it ¹.

Potential causes raised by the community: a throttle position sensor (TPS) signal loss or grounding issue — specifically, poor contact to ground at the TPS can cause this, based on a similar case on a different vehicle ⁴⁵⁶; a MAF (mass airflow) sensor fault; a coolant/ДТОЖ temperature sensor feeding false readings to the ECU, causing a false "cold start" enrichment; or a blocked/dirty crankcase-ventilation hose ⁷⁴. A computer diagnostic scan can show the throttle position and other live values to narrow this down ⁸⁹. Suggested remedies, in rough order of being tried: a full diagnostic scan first; throttle-body cleaning (a dealer throttle-wash appointment was booked in this case); DTOZH/MAF sensor replacement if the scan points there ¹⁰¹¹¹². Note: in this specific case the temperature gauge itself displayed normally throughout, which the owner treated as evidence against (but not proof against) a coolant-sensor cause ¹³.

Conflict: multiple plausible causes were debated without an on-record confirmed fix in this thread — throttle sensor, DTOZH, MAF, and crankcase ventilation were all raised, and a diagnostic scan was recommended to narrow it down rather than guessing ¹¹¹⁶⁸.

Baseline healthy idle parameters, for comparison. As a reference point for what a normal, non-floating idle looks like: on a healthy 2019 model-year (post-facelift) engine, cold idle sits around ~930 RPM with 21.3% engine load as read on an OBD2 scanner, with the lambda-sensor reading near stoichiometric. Owners troubleshooting floating/surging idle can use these figures as a rough sanity check against their own OBD2 readings ¹⁴¹⁵.

Revs rise by themselves when the clutch is pressed. An owner describes a video in which the engine revs on its own when the clutch is pressed, with no throttle input. Advice: switch off, remove the intake hose at the throttle body and check the throttle flap position, since debris under the flap can hold it open¹⁶¹⁷.

Related pages

• Camshaft position sensor — P0340 and oil seal
• Crankcase ventilation hose and rough idle
• MAP sensor part number — cleaning fix
• Idle stalling/shaking at stops — likely air-intake leak
• Oxygen sensor — diagnostics and alternatives

Sources

This page is compiled from 17 community messages. Every fact carries a numbered reference to its original author and message.

Last updated: 2026-10-29