Surging Idle Question

[Lifted94XLT]

Vehicle in question is a 92 Coupe w/ 87 5.0 converted to mass air w/ X-cam. The rest of the engine specs are in my sig if any of that matters with this issue.

I have gone thru the entire Surging Idle Check List a couple times now and everything it checking out.... I have a new IAC, new TPS, new MAF, the MAP isn't new but I am not gettin a MAP code, my timing is set at 14* w/ spout out. TPS setting is at .998v. I have checked and cleaned all my grounds. I have a 3g Alternator and I have stepped up to a 2ga ground wire from block to frame and everything that is supposed to be done to support a 3g upgreade. When I initially start the car it will idle great, no matter how long you let it sit there, but as soon as you put a load on it, it will start surging. It starts small, just a couple hundered R's or so, then progressively gets worse until the car dies. I have tried what I believe is everything. I built this entire car myself, so I am pretty mechanically inclined, however, I'm not the best at diag. Does anybody have any suggestions of something that maybe I have overlooked. AS i said above, I have already went over the Surging Idle Check List so please don't just link my to that thread.

Thanks for any help you can give.

--Ryan

 

[BlackGT89]

I know the check list mentions the 10-pin connectors, but did you actually take them apart and clean them the recommended way ? A lot of important info is relayed between the engine and computer to through those conectors. Last time I degreased my engine I think I got water in mine and had to re-clean them again.

 

[Lifted94XLT]

I know the check list mentions the 10-pin connectors, but did you actually take them apart and clean them the recommended way ? A lot of important info is relayed between the engine and computer to through those conectors. Last time I degreased my engine I think I got water in mine and had to re-clean them again.

I did clean them, twice. but it was so long ago, I don't remember how i did it.... haha, I'll add that to the "to try" list though. Thanks.

--Ryan

 

[jrichker]

I am the guy who created "Surging Idle Checklist , so I will do my best to help you.

According to the information I have, the idle quality/low speed perforamce of the X303 camshaft is not as good as the stock camshaft. It does offer more high RPM power than the stock camshaft.

Have your tried clocking the MAF, that is, rotating the MAF housing while the engine is surging to see if it will smooth out?

If you cannot get good idle when setting the base idle speed, as describled in post # 2 of "Surging Idle Checklist you may have mechanical problems like vacuum leaks and misadjusted valves.

 

[Lifted94XLT]

I am the guy who created "Surging Idle Checklist , so I will do my best to help you.

According to the information I have, the idle quality/low speed perforamce of the X303 camshaft is not as good as the stock camshaft. It does offer more high RPM power than the stock camshaft.

Have your tried clocking the MAF, that is, rotating the MAF housing while the engine is surging to see if it will smooth out?

If you cannot get good idle when setting the base idle speed, as describled in post # 2 of "Surging Idle Checklist you may have mechanical problems like vacuum leaks and misadjusted valves.

Alright, I ran outside real quick to mess with the car for a minute. I can't get too into it as this car is the only thing I have to drive right now as my DD's engine locked up on me. I started the car and it idled fine for about three minutes, then I idled it up tryin to get it to start surging. My trick worked and it started, I then proceeded to clock the MAF both directions (clockwise and counter) with no avail.... I didn't reclean the salt and pepper shakers though....

I'm wondering if maybe the MAP/BARO is bad though. its from the 87 speed density car and has not been replaced. Is there a way to test it to see if its good or not before I spend $75 for a new one, and to also help me narrow down the issue?? this thing is hard enough to drive in traffic, much less a surge at idle, so I have been driving with the MAF unplugged to put it into "limp mode" cause it at least idles smooth (or as smooth as it can for the size lift cam I have)..... And we all know limp mode sucks cause it sucks down the fuel, but sadly I have no choice at this time.

Thanks
--Ryan

 

[jrichker]

MAP/BARO sensor operation and code 22

Revised 19-Jul-2011 to add functional descriptions for MAP and BARO operation.

On a Speed Density car, the MAP/BARO sensor is connected to the intake manifold and acts to sense the manifold pressure. Lower vacuum inside the intake manifold when combined with more throttle opening measured by the TPS means more airflow through the engine. As airflow increases, fuel flow through the injectors needs to increase to keep the air/fuel ratio where it needs to be. When manifold vacuum increases, the engine is either decelerating or idling, and it needs to reduce the fuel flow through the injectors.

On a Mass Air car, the MAP/BARO sensor vents to open air and actually acts to sense the barometric pressure due to changes in weather and altitude. Its purpose is to set a baseline for the computer to know the barometric pressure. As barometric pressure decreases, it leans out the fuel flow to compensate for less oxygen in the air. When the barometric pressure rises, it increases to add fuel since there is more oxygen in the air. The fuel requirements decrease as altitude increases, since the atmospheric pressure decreases.

Disconnecting the MAP or BARO sensor will set code 22.

Misconnecting the BARO sensor to vacuum on a Mass Air car will cause the computer to lean out the fuel mixture.

Code 22 or 126 MAP (vacuum) or BARO signal out of range. The MAP or BARO sensor is pretty much the same sensor for both Mass Air & Speed Density cars. The main difference is where it is connected. Mass Air cars vent it to the atmosphere, while Speed Density cars connect it to the intake manifold vacuum. Its purpose is to help set a baseline for the air/fuel mixture by sensing changes in barometric pressure. The MAP or BAP sensor puts out a 5 volt square wave that changes frequency with variations in atmospheric pressure. The base is 154 HZ at 29.92" of mercury - dry sunny day at sea level, about 68-72 degrees. You need an oscilloscope or frequency meter to measure it. There a very few DVM’s with a price tag under $40 that will measure frequency, but there are some out there.

The MAP/BARO sensor is mounted on the firewall behind the upper manifold on 86-93 Mustangs.

Baro or MAP test using frequency meter - run the test key on engine off. The noise from the ignition system will likely upset the frequency meter. I used a 10 x oscilloscope probe connected from the frequency meter to the MAP/BAP to reduce the jitter in the meter's readout.

If it is defective, your air/fuel ratio will be off and the car’s performance & emissions will suffer

Some basic checks you can make to be sure that the sensor is getting power & ground:
Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter.
Check the resistance between the black/white wire on the MAP/BARO sensor and then the black/white wire on the EGR and the same wire on the TPS. It should be less than 1 ohm. Next check the resistance between the black/white wire and the negative battery cable. It should be less than 1.5 ohm.

The following power on check requires you to turn the ignition switch to the Run position.
Use a DVM to check for 5 volts on the orange/white wire. If it is missing, look for +5 volts at the orange/white wire on the TPS or EGR sensors. Use the black/white wire for the ground for the DVM.

 

[Lifted94XLT]

Looks like I'll be able to do a power and ground check on the BARO, but guess I'll have to find an oscilloscope to actually test it..... sounds fun. Haha.

I'll get this tested (at least power and ground), clean the S&P Shakers, and RE-set base idle and post my results....

... ever feel like you're running around in circles?

 

[Lifted94XLT]

a buddy of mine is gonna let me borrow a BRAND NEW BARO sensor this weekend. figure that's the best way to test mine without an oscilloscope. I also just received an EGR delete plug from RJM Injection Tech that plugs into the factory EGR plug and fools the comp into thinkin the EGR is there and closed. I doubt that will help anything, just documenting what I'm doin for everyone.

I do have another question though. my car was originally a Cruise Control car that I have sense removed but the VSS is still there and plugged in.... would this have any negative results, even if its good? and also, is there a way I can test it to see if it IS good? thanks.

--Ryan

 

[RangerJoe]

I know its in Joe's explanation above...but you don't have a vacuum line hooked up to the bap do you? On a mass air system it senses from the atmosphere.

Good luck!

 

[Lifted94XLT]

Yes sir. There is no vacuum line connect to the BARO

 

[Lifted94XLT]

Ok y'all. I did some tinkerin last night and got some interesting results.

I sanded down the metal behind the computer ground next to the computer, I turned the IAC upside down and upped the idle to about 1100 rpm and the idle surge went away...

I turned the IAC upside down b/c w/ it in the factory orientation and unplugged, the car idled around 600rpm. According to the Surging Idle Checklist, it states that it should idle around 1000 with the IAC unplugged. I turned it upside down and it started idling about 1050-1100 with it unplugged. I then plugged it back in and adjusted the idle as low as I could go without it surging and thats how I got my 1100 rpm idle setting. I then checked the TPS voltage, it was at .94v so I bumped it up just a touch to .964v. I then reset the computer. After about 40 minutes of me gettin side tracked on another project, I reconnected the battery and started the car.... it idled at about 1500 on initial start up then slowed down to 1100.... I let it idle for about 5 minutes, periodically revving it up with no surge. I then took it out for a spin with a lot of start and start traffic driving, highway drivings, and just kinda beating on it to put it through about every situation it could be in.... It was periodically surge but only about 50-100rpm.... I drove the car all night in the same situations, starting and shutting off the car four or five times with no problem. the wierd thing is that when I came home last night.... I let it idle in my driveway for a minute before I shut it off and it started surging really bad!! about 1500 rpm bad! i shut it off and went inside, pissed off, and went to sleep... I haven't went back out today yet, just thought I would post up my findings from yesterday.

One more thing, Everytime I push in the clutch, it will rev up to about 1600-1800 rpm til I come to a complete stop and then idle down to normal. I'm thinking that it may be because the car originally had cruise control which I have since removed, but I still have the VSS plugged in.... could that be causing this? Thanks guys.

--Ryan

 

[jrichker]

The set base idle speed at no point suggests that the idle should be 1000 RPM.

Here's what it does say...

OK, now you have gone through the list and eliminated most of the possible problems. Now your mechanical and electronic problems are fixed, you can set the base idle speed.
Setting the base idle speed:
First of all, the idle needs to be adjusted to where the speed is at or below 600 RPM with the IAC disconnected. Then the electrical signal through the IAC can vary the airflow through it under computer control. Remember that the IAC can only add air to increase the base idle speed set by the mechanical adjustment. The 600 RPM base idle speed is what you have after the mechanical adjustment. The IAC increases that speed by supplying more air under computer control to raise the RPM’s to 650-725 RPM’s

Remember that changing the mechanical idle speed adjustment changes the TPS setting too.

This isn't the method Ford uses, but it does work. Do not attempt to set the idle speed until you have fixed all the codes and are sure that there are no vacuum leaks.

Disconnect the battery negative terminal and turn the headlights on. Leave the battery negative terminal disconnected for 5 minutes or so. Then turn the headlights off and reconnect the battery. This erases the computer settings that may affect idle performance.

Warm the engine up to operating temperature, place the transmission in neutral, and set the parking brake. Turn off lights, A/C, all unnecessary electrical loads. Disconnect the IAC electrical connector. Remove the SPOUT plug. This will lock the ignition timing so that the computer won't change the spark advance, which changes the idle speed. Note the engine RPM: use the mechanical adjustment screw under the throttle body to raise or lower the RPM until you get the 600 RPM mark +/- 25 RPM. Changing the mechanical adjustment changes the TPS, so you will need to set it.

When you are satisfied with the results, turn off the engine, and re-install the SPOUT and reconnect the IAC. The engine should idle with the range of 650-750 RPM without the A/C on or extra electrical loads.

An engine that whose idle speed cannot be set at 600 RPM with the IAC disconnected has mechanical problems. Vacuum leaks are the #1 suspect in this case. A vacuum gauge will help pinpoint both vacuum leaks and improperly adjusted valves. A sticking valve or one adjusted too tight will cause low vacuum and a 5"-8" sweep every time the bad cylinder comes up on compression stroke. An extreme cam can make the 600 RPM set point difficult to set. Contact your cam supplier or manufacturer to get information on idle speed and quality

 

[Lifted94XLT]

Bottom of Post #2 on Surging Idle Checklist Thread

Ranchero5.0’s comments on engines with other than stock cams:

A little dragon slaying lore here

99% of the time on a cammed car opening up the divider between the ports on the IAC with a dremel so the motor idles at 1000rpm with the IAC unhooked, the throttle plate shut and the TPS at .98vdc fixes all surge related problems. Found about to do that on my '93 with a very mild cam and good induction it didn't like idling below 900rpm. The IAC can't react quick enough to a lopey cam induced RPM fluctuation so instead of dampening the surge it increases it. Every E cammed car I've ever worked on needed this to keep a stable idle. Similar to Fords idle bypass plate without the cobbled look. Just dremel out a little at a time till it idles around 1k. In my experience the stock puter doesn't like to idle a cammed car down low.

If that doesn't do it check the 12vdc to the heater on the O2's. One smack of wiring on headers wipes out the fusible link hidden in the wiring on the engine side of the firewall where the main puter harness goes through. This will cause the o2's to slowly go out of tolerance and the puter flips out. check this if the car's running really rich a idle too. Ranchero got nailed when first installed and the '93's done it too. I actually ended up soldering on a stereo inline fusible link and installing a 20a fuse to make the repair quicker.

For an elaboration on the o2's. The two white wires on the o2 sensor are for a the o2 heater. Without them working ,especially on long tubes the o2's cool off at idle and slow cruise and stop working correctly and the puter flips out. Use a paper clip or two and check for 12dvc between the two wires. No voltage, no heaters. Ford actually made a change and put the fusible link on the outside of the harness in the early 90's

More to come as I get time...

Jamie

That's where I got the info on the 1000rpm idle with IAC unplugged.

 

[jrichker]

Try the process I posted first. If it does not work and you have no codes or vacuum leaks, then try the procedure posted by Ranchero5.0. Settting the base idle speed above the factory 650-725 RPM is a case of last resort.

 

[Lifted94XLT]

Try the process I posted first. If it does not work and you have no codes or vacuum leaks, then try the procedure posted by Ranchero5.0. Settting the base idle speed above the factory 650-725 RPM is a case of last resort.

Ok, I will try setting the base idle again... I know I tried re-setting it in the past with no luck, but I'm always willing to try something a second, third, or fourth time just in case. Haha. I'll post my findings when I get it done.

--Ryan

 

[FoMoCo17]

Not meant to hi-jack the thread here, but will O2 sensors w/o the heaters working show a code that comes up with a code scanner in the KOER test?

 

[JungleJoe]

Man, I'm going throught the exact same thing as you are Lifted94 right now....its insane.Iv done EVERYTHING in the that check list myself...going to try couple more things, then its off the the dealership to get a checked out!

 

[FoMoCo17]

Add me to the list!

 

[Lifted94XLT]

Its a headache isn't it? Lol... I still haven't had a chance to re-set base idle yet.... Being a daily driver, by the time I get it home, i don't wanna touch it. I'm goin outta town this weekend too, but i will report back as SOON as I get it done.

 

[FoMoCo17]

Yes, your absolutely right, I do not want to touch mine anymore ... but i cannot stop ... its gotta get fixed!