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Discussion summary
YOUR RESEARCHLow Idle Issue
Leading reported evidence
Check vacuum hoses
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Suggestion
Check all the vacuum lines that attach to the intake (ensure not cracked) and the hose clamps that secure the intake pieces together, mine were looser than I liked.
Leading evidence: 'Check vacuum hoses' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Check vacuum hoses' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Suggestion · Original poster
Loren - I bought some carb cleaner and cleaned the throttle butterfly as well as I could.
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Suggestion · Original poster
filling the tank), it will be back to 800 and solid as a rock when the car is restarted.
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Suggestion
It might run a little uneven initially (do to the cleaner) but then it should even out and idle smoothly.
These are separate views of the same evidence. Frequency alone does not establish a fix, and these counts must not be added together.
Check vacuum hoses
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Discussions that contain suggestions
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion
Check all the vacuum lines that attach to the intake (ensure not cracked) and the hose clamps that secure the intake pieces together, mine were looser than I liked.
Counts describe captured discussions, not unique people or a diagnosis. Author identities are not reliably stored. Exact duplicate evidence is counted once across matching discussions; one discussion counts at most once per action/state. Multiple repairs reported together remain a combination. Suggestions and failed attempts do not establish a fix. Matches cover whole discussions and can include related faults, model variants and incomplete threads.
9 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
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Generation: 20261026T181445Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
I have a '99 C4 with 73k that is having idle issues intermittently. Usually it sits at 800 RPM's with no problem. It is typically fine when started and the problem begins to occur after driving several miles, when the car is fully warmed up.
When I stop at a light the RPM's will drop to 700 and most recently as low as 600. There is an occasional surge to the 1,000 range, but that is the rare exception. It seems to get increasing worse with lower temperatures. (It has been in the single digits in Chicago for the last few weeks). If I turn the car off for a few minutes (e.g. filling the tank), it will be back to 800 and solid as a rock when the car is restarted.
There are no codes. I have cleaned the MAF and the throttle body as well as I could without removing it from the car and disassembling it.
I have searched the archives and am unable to come up with anything conclusive to check. I'm stumped on this one.
Any ideas of where to start looking? I am using a stock air filter that has been in the car for about 15k and could probably stand to be replaced.
Any ideas or suggestions? I have the durametric tool if readings would help.
Thanks in advance.
My car is a tip and it always idles at 600RPM. Check all the vacuum lines that attach to the intake (ensure not cracked) and the hose clamps that secure the intake pieces together, mine were looser than I liked.
Maybe time to clean the throttle butterfly.
On egas cars the throttle butterfly controls the idle air so it is sensitive to carbon and dirt build up.
Buy some spray carb or fuel injector cleaner then remove the air cleaner and intake tube so you can get at the throttle body. Open the throttle with your finger (engine off) and spray the cleaner all over inside the throttle body and butterfly. Remove all the black carbon build-up until you see shiny metal.
Reinstall the intake tube and air cleaner and start the car. It might run a little uneven initially (do to the cleaner) but then it should even out and idle smoothly.
I like to run a bottle of Chevron Techroline through the gas every 3-5,000 miles just to reduce the carbon build up.
Thanks for your help and advice everyone!
It seems to be worse when it is extremely cold - perhaps the A/C is cycling off?
Loren - I bought some carb cleaner and cleaned the throttle butterfly as well as I could. I think I got 99% of the carbon off the butterfly area - the inside of the throttle body is still pretty black. The only inconsistency I notice is that I can maually push it another 1/8"-1/4" after it has springed back to the 'closed' position. When released it springs back the 1/8"-1/4" that I pushed in. Does this make sense?
Most recently the RPM's have been low from a cold start as well. When started the car will idle at 800-900 rather than the usual 1,200. After a few seconds they will build up to 1,100 or 1,200.
If this is a recent problem and on the same tank of gas, also consider if you may have got a batch of bad gas. Any obscure places you filled up at lately. I just ran a batch of gas inj/cleaner additive and I swear it made a ton of difference in idle and smoothness over all.
Just a thought,
RB
