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Bouncy idle when cold

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Old 01-08-2012, 07:22 PM   #1
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Default Bouncy idle when cold

Greetings all,

First, this forum has been a lifesaver - I've been lurking off and on for years but so far have been able to find the answers to everything I need without actually posting. Now, I'm stuck and I need some help!

Car: 1995 Integra LS, stock everything. 178K miles, had it since it was brand new.

Symptoms: When cold, the idle starts out high, then as the car warms the idle begins to drop, but it bounces around between 1000-2000 RPMs until it warms up, then everything is fine. The bouncing is a little faster than once per second. I ingored it for a year, since it used to only happen in Park and Neutral. Now it jumps even in gear and driving is unsafe until it warms up. In the service manual, it shows the idle speed vs. temp during startup. It starts out flat at higher RPM until the temp gets to about 70 deg F, then ramps down until the temp gets up to 176 deg. It's during this ramp down that the bouncing occurs.

I have done the following:
- looked for vacuum leaks. Can't find any, but not sure I checked them all.
- cleaned the IACV and throttle body with carb cleaner. Seemed to work fine, but next day same problem.
- cleaned the IACV again, more thoroughly. No improvement.
- replaced the IACV $$$. No improvement.
- sucked about 2 oz Seafoam in through the main vacuum line that feeds the rear of the throttle body. Added fuel injector cleaner to the gas. No improvement (I've only driven it two days since this).
- checked the PCV valve, it seems to move freely.
- remove and cleaned the FITV by this procedure: No improvement. I did notice that when I cover the port in the throttle body that feeds into the FITV the RPM drops to about 1000 and stops bouncing, but I'm not convinced the FITV is to blame since it seems to be moving just fine inside after cleaning.
- unplugged the O2 sensor. No improvement, still bouncing away like crazy.

I'm really glad I didn't pay the mechanic $700 to replace the IACV, since that clearly didn't fix the problem. Any ideas? I keep reading on the forums that the most common problem is a vacuum leak, but I'm not sure which hoses to check other than the ones that feed into the back of the throttle body - are there any others to look for? It seems like a vacuum leak would affect more than just during the warm-up. Thanks in advance!

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Old 01-08-2012, 08:01 PM   #2
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Default Re: Bouncy idle when cold

how did you check for vacuum leaks? just visually? if so, that won't help. use a bottle of quick start. spray around any vacuum lines, intake manifold, throttle body area. if the idle jumps when you spray a particular area, that's where it's leaking.
check for collapsed vacuum lines as well.

also, try checking resistance of the coolant temp sensor. first cold, then hot. or disconnect it altogether. see if it changes on warm-up
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Old 01-11-2012, 04:36 PM   #3
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Default Re: Bouncy idle when cold

Thanks for the quick reply and the tips on checking for vacuum leaks. I had almost given up when some overheating issues yesterday made me do a forehead-slap. I know that I have a radiator leak (taking care of that this weekend) but for some reason it didn't occur to me to check the coolant level. Evidently it was low enough that I wasn't getting good flow to the IACV and FITV during idle. So, while replacing/cleaning these improved things, the problem wasn't totally gone. Once I topped off the coolant, everything started working fine.

So, if anyone reading this in the future has the bouncy idle problem, CHECK YOUR COOLANT LEVEL in addition to the vacuum leaks, IACV, and FITV.

Good luck, and happy Honda-ing!

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2000, 95, acura, bouncing, bouncy, cold, honda, idle, integra, reading, rpms, ruckus, stop, tl, vacuum

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