87 r10 big cam, idles high

[tater502]

I traded my 93 for this 87, someone put a bigger cam(dont know the specs) and chip (motorvation 777) in it. When I first start it the idle is normal and I can really hear the cam, after a few seconds it idles higher and doesnt come down. Stock air filter and exhaust, no converter. No codes.

Ive replaced the fuel filter, pcv, plugs(old plugs were black), wires, cap and rotor, throttle body gasket, tps, iac, water temp sender, and looks like the O2 sensor was replaced too.

Before I go through all the trouble buying a stock cam cam and computer is there anything else I should check/replace? Timing or?

[kelsfine69]

Check the TBI gasket, Common for sucking in.

[tater502]

Originally Posted by kelsfine69

Check the TBI gasket, Common for sucking in.

Thats the first thing I did. Ive done tons of searching everywhere, the only thing I can think to do is put it back to stock.

[rfmaster]

It sounds like you may need to reset IAC - use a search function - I have posted several times how to do this.

Other possibility: Intake manifold leak (check PB line, PVC lines for cracks). The worst possibility is intake leak sucking in from inside engine - this is common when incorrect intake manifold gaskets are used. TBI ECM stock code can handle most mild RV grinds without reprogramming as long idle vacuum is around 16 to 18 in-Hg.

//RF

[tater502]

I reset the IAC when I put it in new, twice just to make sure. Al the vacuum lines look good, I sprayed carb cleaner on all the lines, fittings and around the throttle body and didnt notice any difference.

From what Ive read the motorvation 777 chip is custom made. The cam is bigger than an rv cam, I will check vacuum and see if its within the 16-18 range.

I was just messing around with the truck and noticed when I step on the brakes the engine goes to the higher idle almost every time. Would a brake booster vacuum leak be causing all my problems?

[Zane M]

Yes, the brake booster leaking could definitely be the culprit.

[3r!c84]

Originally Posted by tater502

I was just messing around with the truck and noticed when I step on the brakes the engine goes to the higher idle almost every time. Would a brake booster vacuum leak be causing all my problems?

plug off the line going to youe brake booster. problem found.

[tater502]

Ok its not the brake booster. That must have been just coincidence.

I reset the IAC again, started the truck and it idled normal, shut off and restarted and its back to high idle. The TPS is getting 5 volts, ground is good, 0.75 volts closed throttle and 4.4 wide open. I unplugged the brown wire near the booster to check timing and the truck died.

I drove it about 25 miles today before working on it. At first it was idling high like it does then all of a sudden it started idling too low and died at every stop.

I dont know if this has anything to do with the high idle but it cranks for a lot longer than it should before starting. Any suggestions?

[rfmaster]

That's the problem with custom chips - you do not know what the base timing should be unless you have documentation. On a stocker it is 0 deg BTDC with EST connector open. Custom chip - it is anyone's guess unless you get a EPROM read. Lets assume 4 to 6 deg (that's what I like to set my base line timing in EPROM and actual).

Recommendation: Reset the base timing (EST open) to 4 deg as it should help with initial fire-up. Just keep an eye on pinging under load. Engine off, reconnect EST, reset codes by disconnecting battery.

On the unstable idle - could be related to a dirty IAC passage. But it has to be very dirty for it to become a problem. Another way to set idle is to pop anti temper cover that protects idle set screw (on the front of driver side of TB). You'll need Torx screwdriver (T25 IRC) and adjust minimum idle to suit your needs. This effectively takes IAC out of the equation unless you have low idle vacuum. Just be aware that smog Gestapo goes nuts when they see anti-temper plugs removed.
When ECM sees low vacuum it will bump up commanded idle to prevent a stall (there is a limit). Before getting too deep into ECM idle logic please check your vacuum hose between MAP and the back of the TB. Nothing else can be connected to that port. A flaky MAP sensor may be the cause of some of these idle issues, but it will set of SES before anything else. Hold of on buying a new MAP.

//RF

[INSIDIOUS '86]

A carb will fix this issue :p.
Try replacing your tps sometimes they will test fine but still be bad.
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[tater502]

I cant check or set the timing because it dies when the brown wire is unplugged. Unless Im doing something wrong?

The IAC passage is clean, Ive taken the throttle body off and made sure everything got cleaned.

I had the idle set screw backed out all the way before and it idled high, I turned it back in some yesterday because it was dying at every stop.

No smog checks here and the tps is new.

This isnt something I cant drive it just bugs me. Ill take a break from working on it and search this site some more. I swear Ive read every thread twice about tbi problems. Im thinking a new cam, computer, and some gaskets might fix the problem. It cant hurt and I dont need a big cam in a daily driver.

Thanks for the replies everyone, Ill let you know if I ever get this figured out.

[rfmaster]

@tater502

The reason why it is dying when you unhook EST plug is that base timing is retarded too much. Larger cams need a bit more base timing to idle. In SBC rotor is turning clockwise, so turn distributor counter clockwise to advance timing. Advance timing 2 to 3 deg a time until engine is idling with EST open. Since we do not know what your cam is I would try to get to idle around 625 to 675 RPM around 4 to 6 deg BTDC (with EST open). Use minimum idle screw to keep idle speed up while you dial in base timing. Engine may lope a lot depending on the camshaft duration and overlap, but it should idle to have a fighting chance. Once you reconnect EST plug timing should jump to about 16 to 20 deg and idle speed should be around 675 to 725 RPM (commanded idle is one of the parameters that a custom tune may have altered to suit the cam).

As for the cam for DD with a flat tappet cam SBC you can not go wrong with CS-1014r - it is a moderate RV grind and wakes up otherwise stock engine. Stock cam is pathetic.

You do not need new ECM, just a different EPROM that matches your camshaft and trany.

//RF

[tater502]

I finally got time to work on the truck. Timing is fine and a new intake gasket didnt help any. Every time I reset the iac it idles normal for the first drive then after restart it was back to high idle.

Last time I reset the iac and jiggled some wires it idled normal and ran perfect for a week. Now I have to step on the gas to start it(cold and warm) and it idles down and dies at stop lights. Im thinking its either the computer or a bad wire. What wires should I check? iac to computer and cts to computer? Any other wires?

[rfmaster]

Originally Posted by tater502

I finally got time to work on the truck. Timing is fine and a new intake gasket didnt help any. Every time I reset the iac it idles normal for the first drive then after restart it was back to high idle.

Last time I reset the iac and jiggled some wires it idled normal and ran perfect for a week. Now I have to step on the gas to start it(cold and warm) and it idles down and dies at stop lights. Im thinking its either the computer or a bad wire. What wires should I check? iac to computer and cts to computer? Any other wires?

There are four wires that used to control IAC (blue-white, blue-black; green-white, green-black). But from your description it sounds like you have one of stepper motor windings intermittent or you have one out of the four pins in the plug making intermittent contact with a socket pin. To test IAC coil windings use an Ohmmeter and check between coil resistance between terminals A and B - it should be greater than 20 Ohms, with most coils measuring between 40 to 80 Ohms. Also measure the second coil between terminals C and D - it also should be within the same range. If Ohmmeter shows very low or high resistance values replace IAC, but make sure that you get good contact between Ohmmeter probes and contacts in the IAC socket.

New IAC is around $30 from RockAuto or $5 from a local JY.

Check if ECM has any codes stored by jumping pins A & B on ALDL connector. If only code 12 is being reported then it would appear that sensors are OK. replacing sensors blindly gets expensive after while!

//RF

[tater502]

Im just testing the iac itself unplugged right? Theres no codes at all.

[rfmaster]

Yes, unplug harness connector. It actually makes it easier to remove IAC from TB and test it on the bench.

//RF

[mrhino]

just thinking out side the box a little, but if the PO had done all this work to it I.E. bigger cam, custom prom and who knows what else. Its not to far of a stretch to think he has done some custom TB modifications and jacked it up. like maybe boring the venturi's or polishing to much. Thus allowing air to slip past the throttle blades. and increase the idle. Just a thought.

[tater502]

Originally Posted by rfmaster

That's the problem with custom chips - you do not know what the base timing should be unless you have documentation. On a stocker it is 0 deg BTDC with EST connector open. Custom chip - it is anyone's guess unless you get a EPROM read. Lets assume 4 to 6 deg (that's what I like to set my base line timing in EPROM and actual).

Recommendation: Reset the base timing (EST open) to 4 deg as it should help with initial fire-up. Just keep an eye on pinging under load. Engine off, reconnect EST, reset codes by disconnecting battery.

//RF

Forgot that you said this, when checking my timing is was at 2 deg and I set it to 0. Ill mess with it tomorrow and set it to 4-6 deg. Seems like it ran a whole lot better before I messed with it.

I took the wires out of the plug going to the iac to check them and broke a couple plastic pieces (the part of the plug that goes into the iac)off it. Seems nobody carries weatherpack connectors local, so Ill grab one from the junkyard for now or see if the one off my 91 is the same.

[rfmaster]

Originally Posted by tater502

Forgot that you said this, when checking my timing is was at 2 deg and I set it to 0. Ill mess with it tomorrow and set it to 4-6 deg. Seems like it ran a whole lot better before I messed with it.

I took the wires out of the plug going to the iac to check them and broke a couple plastic pieces (the part of the plug that goes into the iac)off it. Seems nobody carries weatherpack connectors local, so Ill grab one from the junkyard for now or see if the one off my 91 is the same.

Get the IAC while you are there. It is a good idea to have a spare IAC. SBC TBI IAC are more or less the same between 87 and 95. There are some minor differences in the head design, but they are interchangeable. BBC is completely different. To replace connector body you'll need this special pin tool



to safely remove pins from the connector body. Do not even try pulling pins out with anything else - you'll wreck connector and damage pins. Available from online outfits - JEGS Performance Products 10769

//RF

[tater502]

Originally Posted by rfmaster

Get the IAC while you are there. It is a good idea to have a spare IAC. SBC TBI IAC are more or less the same between 87 and 95. There are some minor differences in the head design, but they are interchangeable. BBC is completely different. To replace connector body you'll need this special pin tool



to safely remove pins from the connector body. Do not even try pulling pins out with anything else - you'll wreck connector and damage pins. Available from online outfits - JEGS Performance Products 10769

//RF

I have that tool, the connector was very brittle. Is there a tool for taking the square connectors, like the water temp sender, apart?

Put a new connector on and reset the iac, idles normal now. Also set the timing, new tires, new brakes, and new wiper motor. Its like driving a whole new truck!

[83GMCK2500]

Originally Posted by tater502

I have that tool, the connector was very brittle. Is there a tool for taking the square connectors, like the water temp sender, apart?

Put a new connector on and reset the iac, idles normal now. Also set the timing, new tires, new brakes, and new wiper motor. Its like driving a whole new truck!

Snap-On / Blue Point TT12KT I own that kit, use it to take all manner of connectors apart. Some you have to fiddle with a little, but they all come apart. A good bright light that is small that you can look down into the cavity with is also handy. Sometimes you can see how the pin is retained in the cavity.