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Discussion Starter · #1 ·
Hi all,
I've been attempting to help fix my mother's 2001 G20 the past few weeks and have hit a wall. It basically alternates between high idle at cold start (2-2500rpm) and the same high idle but jumping up/down about 200rpm once warm.

I've also noticed that when driving at around 30mph if I coast it will slowly accelerate up to about 45mph all by itself. I don't know enough to tell if that is a symptom of the high idle while in gear, or if that is an unrelated issue.

We've had it at a shop who replaced the IACV, swapped the MAF, and patched a hole in the air intake hose before the throttle body. Finally, they just told us they could not get it running correctly and suggested we take to a dealer. I've already sunk some money into it and we are pretty close to just selling it as-is, but it drives me nuts to be beaten by such a seemingly silly problem on a car that is otherwise fine.

Any ideas are greatly appreciated!! (especially ones that don't cost a ton of $--ha)
Thanks!
 

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Im new to these car as well, but have you tried the 're-learn' procedure for the IACV after installing the new one? Heres the procedure I found in another thread on this forum..

PRE-CONDITIONING
NCEC0503S02
Before performing “Idle Air Volume Learning”, make sure that all of
the following conditions are satisfied.
Learning will be cancelled if any of the following conditions are
missed for even a moment.
I Battery voltage: More than 12.9V (At idle)
I Engine coolant temperature: 70 - 95°C (158 - 203°F)
I PNP switch: ON
I Electric load switch: OFF
(Air conditioner, headlamp, rear window defogger)
On vehicles equipped with daytime running light systems, if
the parking brake is applied beore the engine is started, the
headlamp will not be illuminated.
I Cooling fan motor: Not operating
I Steering wheel: Neutral (Straight-ahead position)
I Vehicle speed: Stopped
I Transmission: Warmed-up

Sounds easy?!

1. Turn ignition switch “ON” and wait at least 1 second.
2. Turn ignition switch “OFF” and wait at least 10 seconds.
3. Start engine and warm it up to normal operating temperature.
4. Check that all items listed under the topic “PRE-CONDITIONING” (previously mentioned) are in good order.
5. Turn ignition switch “OFF” and wait at least 10 seconds.
6. Start the engine and let it idle for at least 15 seconds.
7. Disconnect throttle position sensor harness connector (brown),
then reconnect it within 5 seconds.
8. Wait 15 seconds.
9. Make sure that idle speed is within specifications. If not, the
result will be incomplete. In this case, find the cause of the
problem by referring to the NOTE below.
10. Rev up the engine two or three times. Make sure that idle
speed and ignition timing are within specifications.
ITEM SPECIFICATION
Idle speed M/T: 800±50 rpm
A/T: 800±50 rpm (in “P” or “N” position)
Ignition timing M/T: 15°±2° BTDC
A/T: 15°±2° BTDC (in “P” or “N” position)
NOTE:
If idle air volume learning cannot be performed successfully,
proceed as follows:
1) Check that throttle valve is fully closed.
2) Check that downstream of throttle valve is free from air
leakage.
3) Adjust closed throttle position switch and reset memory.
(Refer to Basic Inspection, EC-106.)
4) When the above three items check out OK, engine component parts and their installation condition are questionable. Check and eliminate the cause of the problem.
5) If any of the following conditions occur after the engine
has started, eliminate the cause of the problem and perform “Idle air volume learning” all over again:
I Engine stalls.
I Erroneous idle.
I Blown fuses related to the IACV-AAC valve system.
 

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Discussion Starter · #4 ·
Update: Just tried the idle air learning again (post-shop, parts replaced etc.) with no luck. I also noticed for the first time the quick jump up and down in RPMs while driving. Only did it for a quick moment, then went away. Very weird. Anyone have an off-the-wall idea or am I pretty much stuck with taking it to a dealer? (somehow I just have a funny feeling they'll say the ECU is shot or something. ha.)
 

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Sorry to revive this but dang it I'm having the same issue. I had a bad IAC valve that I bought from eBay (never again) so I had to press the gas to turn car on. Long story short, I bought an OEM valve and installed it. Now I'm having the same issues as op. Idle goes up and down constantly and the relearn process is not working. Any ideas?
 

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I had this same exact issue about two months ago. The mechanic that fixed the car replaced the iac which I new needed to get replaced. The computer however was the main culprit. It was sending mixed messages to the engine that was causing it to not know how much air it was getting. Totally fixed now and the car runs great!
 
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