rick_the_mick

Hi all,

I read somewhere that cleaning out the throttle body on these models would sometimes really help performance. Would appreciate it if someone would post/repost how to do this.

brubenstein

Cleaning out the throttle body and the portion of the intake manifold right behind it will primarily help idle and off idle perfomance (the engine will be smoother at idle). Overall performance would require cleaning the intake manifold all the way to the heads, and you have to take apart much more to do this really well.
To do a basic throttle body clean:
- Remove the cast elbow that is attached to the front of the throttle body (3 bolts with 12mm heads.
- Slide the elbow out of the way enough to be able to spray throttle body/injector cleaner into the throttle body.
- Rotate the throttle plates to be able to clean the back of the throttle plates.
- Do not spray the throttle position switch (on the righthand side of the TB).
- As you spray the cleaner into the TB/intake manifold large amounts of black crud will pour out.
- If you can get something like a baby bottle brush you can scrub deeper into the intake maniflod.
- Wipe the inside of the TB and throttle plates with a clean rag so there are no deposits on them.
- clean the mating surfaces of the TB and elbow and put a very thin coat of RTV onto one side (try to find one that says, "safe for 02 sensors"). You don't want an air leak here.
- When you start the engine, push the accelerator to the floor like you would do to start a flooded engine, because there will be cleaner in there.
- The idle will probably now be high and you'll have to re adjust it back down.

rick_the_mick

That looks like a very good description on how to do it. Might it remedy an off-idle stumble (only when cold) condition my '91 GXE has developed?

Jeff92se

iTrader: (82)

Cleaning the TB is always a good idea but if you car stumbles only when cold then I kinda doubt it's the TB. Something in the cold idle circuit is not right. Could be something like a coolant temp sensor... etc.

Does it still go into "fast idle"? Does it still stumble despite being in "fast idle"?

rick_the_mick

Thanks for the cold stumble response. Car starts fine, idles OK, but when the accel. is depressed when cold it stumbles badly, lurches, then clears its throat and roars away.

Jeff92se

iTrader: (82)

You mean it goes to "fast idle"? I assume yes. Hmmm.. try finding the coolant temp sensor and undo the connector. See if it's corroded. Clean it and see if that helps. If not, we are going to have to dive deeper. ie.. fuel filter, MAF, plugs, dist cap, plug wires, pcv valve.

rick_the_mick

I'll go through those items and hopefully find the cure.

brubenstein

If there are deposits on the back of the throttle plates and in the TB, right behind the plates, not enough air can pass at idle. The idle up circuit will try to compensate for this with a higher than normal duty cycle. Once the deposits build up to the point that idle up circuit can't compensate, the idle will drop too low from any added load on the engine.
A clean TB is one of the things you need for proper idle and off idle running. The other primary thing is a good healthy spark, at the right time.

brubenstein

Idle air control valve perfection q45tech
(52/M/Atlanta, GA) 4/26/01 7:15 am
Nissans all have IAC, the trick is to have everything clean enough so that the base idle is correct with 10-15-20% IAC duty cycle then any extra load [PS, AC, Alternator has plenty of room to increase duty cycle and maintain the correct rpm. [Momentary drops when the load increases are normal but the idle speed should return to the same spot [+- 25 rpm] within 1 second as ecu increases duty cycle]....AC on will increase duty cycle from 10 to 30%, headlights and sudden PS movement even more, defrosters, sunroof/windows any abnormal electric load due to the changing HP requirements of the alternator [0.5 to 3 HP].
Unfortunately only the Consult can show the duty cycle.
The 90-95 warm up rpm is controlled [like most cars] with a thermospring /wax combo [heated/cooled by circulating coolant] which [expands/contracts] opening the throttle a little in a sense overridding the ecu base idle speed.
Water temp must be at or above 174 F to get out of the warm up mode allowing full control by ecu.
We have a rule that the warm up circuit not be adjusted since the proceedure is very time consumming, but have seen work by unknowledgable techs who don't know better and attempt to correct other problems by misadjusting this....it can take hours and hours to restore a few turns of a screw since you have no way to get a hot engine cold [down to 0-20F] in summer!!!!!!!!!!!
When you clean throttle body, plenum, intake runners, valve stems, and combustion chambers as well as you can, you are ready to set the IAC to 15%.....then every mile you drive thereafter as the dirt build up the IAC will creep higher.....when a little slim forms under the throttle plate it goes higher when cargon forms on the intake valves it goes higher.....in 5,000 miles from perfect you'll se it up to 30% indicating 15% less air than normal flowing through the throttle body at idle.
When it is very hot under the engine the air is less dense so you would expect the IAC to increase it's duty cycle a few % from 68F ambient to 95F ambient......again watch out for misadjusted cold idle as the cam may decrease manual opening a little when the water goes up to 195-205F requiring more IAC.
When the barometer changes the air density changes, so a 1000 feet is 3.3% [more air to idle].
Techs don't spend the time to correct everything because you won't pay.....setting a correct/incorrect idle with a dirty intake is a nono but it is done all the time.
When you have a weak battery/alternator the ecu will attempt to raise idle to give it the voltage it needs if the IAC doesn't have enough range left it will increase injector duty cyle a few [0.1-0.3] milliseconds but this is tempered by the O2 sensors.
Any atempt to set idle speed with the manual screw on the IAC is really a shot in the dark and will not provide the correct range without the cleaning proceedures first!!!!!!!!!!!!!!!!!

Jeff92se

iTrader: (82)

He said it only idled bad when cold. If it's the TB only it should idle bad all the time.

rick_the_mick

...I'll do the TB clean with the bottle brush but also do the electrical stuff, except possibly the MAF just yet. What does one of those go for?

brubenstein

One thing at a time. Start by getting everything that gets worn out or dirty with age replaced/clean:
TB
Plugs
Wires
Cap
Rotor
Air filter
Gas filter
PCV valve
leaky vacuum hoses
When all of these are good, then see if there are any driveability issues. MAF's are expensive and usually just the connector is dirty. First get the basic stuff right.


A somewhat dirty TB will give a bad cold idle because the idle up circuit can't provide enough air to make up for the dirty TB and also raise the idle.

rick_the_mick

Did all these things this evening, and the car idles smooth as silk. Does idle a tad faster. Seems to have more power too. Won't know about the cold off-idle stumble until it cools down again.

I got three little round oil journal brushes (1/4, 3/8, and 1/2 inch dia.) at the parts store and they're really great for getting in the tight corners around the throttle plates. Thanks for the help.

brubenstein

Glad to hear it.
The idle speed almost always goes up after cleaning the TB. In fact, the base idle speed may well be higher than it should be. The idle screw gets tweaked by people, over the years, to bring the idle speed back up to spec instead of cleaning the TB.

rick_the_mick

I thought the car ran better after I put all the parts on and cleaned the TB, but my wife told me that the problem still existed after it cooled off.

Starts fine, goes to fast idle, but when you go to drive off it stumbles badly. Doesn't do it warm.

O2 sensor? Cold temp. sensor?

superdesi

I am planning on cleaning out my throttle body this coming weekend.

I want to be careful not to spray the throttle position switch. Where is this switch located? Is it inside the throttle body or outside?

I looked in my FSM but could not find the exact location.

rick_the_mick

Facing a VG motor (SOHC as found on the GXE model) from the front, the throttle position switch is on the right side (outside) of the TB. There's a plastic plug that connects wires to the position switch which I had to undo on my car to get the cast elbow attached to the front of the TB off. The plug can be removed by releasing the wire clip that goes around its outside edge.

Jeff92se

iTrader: (82)

So I guess it's back to my theory again.

Check the coolant sensor switch and clean the contacts.

brubenstein

Do you happen to be using Bosch spark plugs?

superdesi

I upgraded to the NGK V-Power BKR6E-11 plugs about 4K miles ago.

Before that I had the NGK BKR6ES-11 (OEM) plugs that were installed when I purchased the car.

I found the NGK V-Power to be of no significant improvement.

rick_the_mick

OK Jeff coolant sensor's next. Where is the little bugger?

Brubenstein, I just put in NGKs on Saturday.

brubenstein

here's a good page on hesitation:
http://www.zhome.com/ZCMnL/PICS/hesi...esitation.html