Help! 97 Q rpm too high when driving with A/C running.

[audiovisiony33]

I had this problem for quite some time and I'm still trying to fix this problem.I have 155K miles now. It stared around 59K miles, as I'm comming to a complete stop I can feel down shift kick pretty bad. (Kick/bump forward)

I thought I need new transmission but when I drive with out A/C I don't feel any down shift kick and it's smooth. It's only noticeable when I drive around about 15 min with A/C running because it holds the rpm up about 850 in gear stopped. When I turn the A/C off after complete stop rpm drops to 650 rpm right away.

Is there any adjustment to lower the rpm when A/C is running? what's causing or controlling the rpm to stay high after comming to complete stop? Some times rpm stays low @ 650-700 with A/C running as I want it to be. But it end up going back up again. Is something getting stuck?

Since it was under warranty. I took it to Metro Infiniti where I bought the car. Only thing I got out service advisor Dave Tanner is it's normal to feel a little kick because it's rear wheel drive. At that time I had LS400 and I have no problem. Has anyone had experienced anything like this ?

[maxnix]

For a 100K you have been tolerating this?

Take it back to the dealer or another one. Yes the IAC can be adjusted, but misadjustment is usually done to cover up some other fault like a dirty intake path, TB, etc. There's a few posts here and in Infiniti Online Mechanic about the intake path and cleaning the IAC, EGR, TB and plenum.

[audiovisiony33]

Thank you for your reply.

I had cerritos infiniti look at it couple of times and told me to pick it up, can't duplicated the problem or normal down shift.

So I've tried to take it on my own and I have tried to lower the rpm with IAC and it works until I drive around at lease 15 min with A/C running.

One time when it reached 850 rpm in drive I turned the IAC knob all the way down to a piont I can't turn no more and wouldn't change the rpm at all.

If there isn't any thing to adjust with I was thinking to go to the junk yard and try another IAC and plenum.

You mension cleaing the EGR. Three month ago I have discovered hissing noise from the rear of the plenum area like vacume leak noise. I couldn't find anything but the little connecting hose under the EGR connecting to metal line was in two pieces. looks like hose exploded. I replaced the hose but still no changes. Looks like I've been driving like that for quite sometimes.

[Q45tech]

Remember idle is the rpm where the parasitic loss from PS, alternator, fan, drag of torque convertor and sometimes AC compressor just equals the power output of the engine.............otherwise the engine would slowly increase in rpm.

The ecu can increase the duty cycle of IAC [adding air which balanced with more fuel] or change ignition advance. Extra air increases MAF voltage minutely and this is noted as a REACTION to ecu commanding more IAC [feedback control] ..........ok rpm is dropping below preset in memory point so I'll add air [and fuel] and see what happens.

Normally AC ON increases injector open time by a few tenths of a millisecond. AND IAC DUTY CYCLE from 10% [how much extra above the amount that flow under TB and the amount that flow thru the IAC manual bypass to maybe 35%.

Dirt and misadjustment is the usual cause.............mechanical things are not as brand new when the software was developed........it does what it knows to do maintain a smooth idle.

AC compressor could be old and worn drawing excessive HP thus more must be created.

The answer would require some time with a Consult II to analyse all the parameters and see the changes AC on off at various temps.

[maxnix]

Hopefully our Bay area members will chime on a better dealer for service.

Seems like you have more than one problem.

[audiovisiony33]

You are right about that. It's been and is a great car. Just some minor things that bothers me. I was about to buy another 00 or 01 Q45 until I found about nico club. Great forum hopefully I will solve the problem soon.Thank You.