Larry1030

My 1999 TL had been sitting out in hot humid southeastern weather for 9 days, then I started it and starting driving. As I slowed for the first traffic light I came to I noticed the engine was surging with my foot off the gas. At the light I put it into neutral and turned off the AC. The engine, instead of idling, raced up to around 2,000 RPM and then slowed to idle, and cycled in this pattern every 2 seconds or so. It kept doing this until the light changed, then I put it in gear and drove around 45 mph with no apparent issues until I came to another stop light. The car at that point idled normally, then suddenly started the cyclical racing again. At that point I stopped and went into a store. I had driven around 6 miles. When I came out of the store the car seemed fine and I drove home with no further incidents.

From the intermittent, suddenly appearing and disappearing nature of the problem, and given that it appeared after the car had been sitting in hot, humid and rainy weather, I gather it is an electrical problem - problem an intermittent or corroded connection on a sensor which somehow affects the idle speed, but I have no idea which one to check, and where the suspect ones are located under the hood. Any tips would be appreciated.

01tl4tl

sounds like time to clean the IACV on the bottem of throttle body,,

and have you removed the intake manifold to clean the egr ports and passages?
thats needed every 75kmiles, and is not in any book~
easy DIY with basic tools and 2 hours of your time

the IAC is a rotating rod with an air slit in it- that moves to control air at idle and idle speed,,it gets clogged and needs a servive
details in our diy section!!
those should fix you up

Larry1030

Thanks very much. Yes, I have removed the intake manifold and cleaned the egr ports and passages; the car has probably only 10k or 15k miles since.

Is the IACV an electrical thingee? The way it suddenly started happening, then went away, then came back and went away again certainly "felt" like an electrical issue. Also, just to be clear, this wasn't the kind of "gently" surging idle I have seen happen with vacuum leaks - this one revved smoothly from idle (around 800 rpm) to about 2000 rpm in maybe a second or two, then suddenly dropped to idle and immediately repeated. If you plotted the rpm vs time it would be a sawtooth wave with a period of a second or two. Does that sound like the iacv?

friesm2000

iTrader: (4)

you have to remember that even thou these cars are over a decade old, they still have really good, and smooth idle control, even when they do develop a vacuum leak (and if anything electrical, i would imagine being a little rougher because, it would not have full control over that IACV motor)

01tl4tl

sure sounds like iacv

cleaned egr system = good!
did you run a metal rod thru the length of manifold to clear the passage?- thats important!!

remove TB for IACV service - remove cover on bottem- release holder tab- remove iacv- clean chamber and rods air slit
its going to be clogged and does exactly as you describe when its getting stuck in the chamber

01tl4tl

we need to make a diy for this and put it in the egr service
they need to be done together - our cars have aged since original info written
and the problems occured

Larry1030

Yes. I actually posted in the thread about the EGR port and you helped me then too - you are one of the best most helpful posters here - thank you. I don't think I touched the IACV when I did the EGR - I don't remember if I removed it from the TB or how I avoided getting the cleaner into it.

Larry1030

I used pipe cleaners saturated with TB cleaner - it was clean, trust me. Now that I recall I also ran a drill bit through the gunk (not big enough to take metal, just gunk) before I ran the pipe cleaners through.

01tl4tl

did you run a wire rod/coat hanger thru the entire length of the manifold ?
from the mouth end of manifold to the openings under egr valve at opposite end
removed egr valve to clean under it- allow wire to push crud out
and lube its operating arm?
not just a great job on the 1 port opening
all that crud coats the passage the gasses move thru

the TB= throttle body- you removed it from manifold -correct?
did you replace that gasket to manifold- if not there is major source of vac leak

IACV to reach it you flip the TB upside down and remove a small round cover plate with 2 screws
remove rubber seal then access the actual rod the electrical impulse moves- to control the amount of air in small amounts at idle
bend tab up- remove rod and clean slit
clean where rod goes too
reasemble

ck for vac leaks

Larry1030

Is this the iacv?

It looks like it might not be too hard to take it off while the tb is still on the car...

01tl4tl

Ive heard it can be done on the car,
not sure it you can get everything clean or just access the round cover to the important part
I figure if you are doing this- the intake manifold is off the car for cleaning the egr passages
then the TB is sitting on the bench- flip it over and service iacv system,
clean air plate and the throttle return springs

if doing egr service- clean and lube the arm on egr valve, clean electrical contacts