lucas240sx

I need help with high idling in my sr.
I've done a lot of researching.

Idle is sitting at 1500 when can is fully counter clockwise.
Idle is at over 2k with cas is in the middle.

I took valve cover off and set it at tdc. Inserted the cas on first dot and insert as it rotates to 2nd dot.

-tps was set at .47v.
-Iacv screw all the way down.
-New both coolant temp sensors.
-All clamps tight on my smic.
-Top 2 vac lines on tb is being used...right for regulator. Left for smic bov and boost gauge.
-With rpm at 1500, vac is around 19.....does this mean if rpm was to be at say 800-900....would the vac drop....which indicates I have a leak?

I let engine warm up, kill it, unplug tps, start car and rev, timing light hooked up to first plug, move cas so timing is at 2nd mark from right.
Rpm then was just as high as it is now

This is driving me crazy



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Kingtal0n

1. find air (boost) leaks as (air) contributes to idle speed (fill the plumbing with 10-15psi of air pressure from the pre-turbo inlet. Block the crankcase off when you do this (I use a marker to plug the valve cover holes))
2. when the timing is right, the CAS will be nearly center.
Use the center wire of the coilpack with the timing light, check it both ways (reverse the pickup) for the orientation that gives you 15* btdc with the cas nearly center. One orientation will give you the wrong timing number, you can always tell because the CAS will be wayyy off center.

ignore the tps and maf for now, focus on the timing and air leaks as these are the two main contributors to idle speed.

lucas240sx

thank you for responding.


so get like a pvc, cover and insert it in the intake boot?
you used a marker to plug the valve cover holes.....how so?
marker on each side of the T for the oil catch can and intake boot.

Kingtal0n

Your rubber intake boot will accept a home depot PVC end cap, in which you will install a valve stem (a typical tire valve stem is fine), and secure it somehow (I used epoxy). Your rubber hoses on the valve cover can be blocked off somehow, I shove a marker into the open ends and hose clamped it down to seal it off. Let air flow against the throttle body, but try to block off the IACV hose with another marker. If an intake valve is open air will get into a cylinder but it is very unlikely it will pass out the exhaust valve (thus lowering pressure) ive never seen that happen.

So the end result is air pressure goes into the inlet, through the turbo, into the hotpipe, through the intercooler, into the cold pipe, and trys to get into the engine (the throttle body is water-tight). The pressure should climb there until 8~psi at which point your rubber inlet boot will begin to blow up like a balloon. This becomes the limiting factor for finding leaks.. however... if you can hold 8psi~ for 15~ seconds in that plumbing then you can be sure most of the leaks are found.

then, open the throttle body and look for leaks at the intake manifold. You should notice a slight pressure drop when you open the throttle body to show that it was holding air back.
Your leak is more likely to after the throttle body (in the intake manifold, or at the intake gaskets, or a hose at the back of the manifold) because a leak in the plumbing prior will not cause an idle speed increase.

from the picture i can tell your timing is wrong, see how the CAS bolts are not really centered? Dont drive it like that, the timing may be 20* too far advanced and it will blow the head gasket. Set your timing right first.

__________________
5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240

lucas240sx

Thank you for the input.
This is an old pic.
I've set the timing to 15 with tps unplugged. ...but the rpm still idles high.
I have a guy coming by tmrw or wed that builds these all the time

In the mean time I'm going to do the boost leak test

lucas240sx

I did replace all the intake manifold gaskets and trq to spec

lucas240sx

I put air to the system to find leaks
Smic setup is good
I have a leak where the iacv meets the manifold, upper and lower manifold mates (small spot) , and a very small leak on tb to manifold.

I really hope this is the reason I have high idle.
I'm going to take it off tonight and mess with it

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unpaintedhatch

If your leak in the IACV isn't the issue maybe it could be a failing headgasket?
hopefully not but something to look out for.

__________________

lucas240sx

It has a metal head gasket and previous owner had it replaced last year

I tighten it all
Rpm dropped to about 1300 with -18 vac
It ran really good
Sounds like I need to check rockers as it sounds like rattling

I'm going to check timing tmrw

Kingtal0n

The diagnostic moral here is that airflow sets the idle speed, the system should be pressure tested, make sure it is air tight i.e. you should be able to shut an engine off by covering the throttle body and similar ports (with your hand for example if you cover the TB/IACV the engine should die, if it kept running you have a leak somewhere)

fuel and timing influence/adjust idle speed, while airflow always sets the idle speed

How to adjust the idle speed on a high performance engine for maximum compliancy (very unlikely to suffer bearing damage due to low idle speeds, which may occur on engines with older ECU or old technology IACV type valves)
1. Get the engine warm, set idle Air fuel ratio, use 15* btdc on sr20det engines with a MAF sensor for best results, allow idle wander up to 22* btdc if you are using a PFC enable "idle timing control", older PFC Units have this permanently enabled.
2. Load the engine with headlights and electric fans, and any other devices you intend to run in the car frequently.
3. disable the IACV somehow; plug airflow holes that lead through any automatic idle control valves so no computer idle speed adjustments can occur for the next step
4. Engine warm and loaded up, set your idle speed using IACV manual adjustment (or throttle body base adjustment if the engine in question has no IACV) 10-60rpm below desired Idle speed.

5. Plug back in (re-enable) the IACV (or computer control) so the computer can use the valve to add that 10-60rpm back into the idle speed to achieve desired idle speed. If the ecu is OEM this is around 850rpm on sr20det. otherwise, units like the PFC have adjustable desired idle speed. If my desired idle speed is 900rpm for example, then my base idle speed with no computer control would be around 860rpm so the computer only needs to add a little bit of air to reach 900. Keeping the two settings (base idle and desired idle) very close will help stabilize the idle of the engine, especially if it has a long duration camshaft.

lucas240sx

With it sitting at 140 deg right now.....my rpm is at 1000 with -14 vac

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Kingtal0n

this doesn't tell anybody anything. 140 degree Fahrenheit is still cold, and cold rpm will vary depending on the wax element in the throttle body cooling loop. If you read the FSM It will explain that sr20det have this wax element for raising the idle of a cold engine, which means your idle could be anywhere from 900-1400rpm in between that. The vacuum seems low. Do a compression test, and write down the exact numbers the best you can (132.5 for example).

Once the engine is warm it should be steady around 850rpm with an OEM camshaft. I dont know what the FSM says about it (I never read it) but once the engine is warm if you follow the above procedure for setting it around 850rpm it should be fine if there are no more air leaks (if the plumbing holds 10~psi of pressure verified).

the reason you do not want excessive high idle is because it absolutely demolishes your fuel economy. The reason we do not want the engine to drop below 800~rpm is because the engine bearings require a certain amount of minimum rotation speed from the crankshaft or else wear will occur. When I cold start, my idle stays around 900rpm and because I have an OEM piston I can drive right away (no boost until the engine is fully warm) to maximize economy you need to spend as little time at exactly idle sitting still as possible. Drivability will suffer if you limit cold start rpm, but drivability is a very minor attribute to me, I am most interested in economy and so use a minimal acceleration enrichment and minimal rpm whenever possible, and also a 15.0-15.2 air fuel open loop cruise area.

My injector duty at 60mph is exactly 6%, and with the turbine disconnected it is 6.5%. There is some measure of fuel economy found with spinning the turbocharger as you cruise, if it is sized for the job. If there is any leak, the turbo will need to spin faster, which means more turbine rpm, which means more exhaust gas pressure resistance to the engine, which diminishes fuel economy and power, as well as pushing the turbo to the right on it's map and limiting max power. A large enough leak will destroy a turbo (imagine you disconnected the compressor outlet from the engine and just ran it open. The wheel would spin so faster it will likely explode) It is therefore imperative that for maximum power and fuel economy, and to minimize turbocharger wear, every molecule of air that exits the turbocharger's compressor makes its way into the engine somehow and does not leak out. This is why we pressure test the entire region to 10-18psi (or more if you need more)

__________________
5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240

lucas240sx

I check for leaks again...find none.
I'll have to try for timing tmrw
I drove it to my grandparents for thanksgiving
Rpm sit at 1400 with -18 vac.

While cruising and little pedal use....wideband leans way out....When I give it gas it will stutter then get going.
While cruising it will go from 11-14....it goes back and forth
Moves from 11 to 14 and go right back down to 11 then moves back up to 14.....continuously

lucas240sx

I changed maf and the rpm went down.
Engine up to operating temp
I'm sitting at right under 1k with -14 vac.
Oil psi at 10.

If I tap the gas....rpm goes up to 1300 and vac to -17 and a/f between 13 and 14

If i give it a good rev...it drops back to around 900 and -12 vac and a/f now it's between 14 andn15

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