Heavy surging under any throttle, then fixed

[BlueCuda]

I started the car up yesterday and as I drove out of the neighborhood it started to surge.  Sometimes it surges at idle as it warms up but this was a surge at any throttle position.  I initially thought maybe my fuel gauge was wrong and I limped to the a gas station and put some in it.  No change, AFR was reading super lean.

The surge was steady in equal intervals, the tach signal always stayed right also.  I opened the hood was was looking things over and all was well.  I reached down and turned it off by unplugging the ECU power while I kept looking things over.  Nothing was out of place so I plugged the ECU back in and fired it up.  It was perfectly fine, I ended up driving it 30 miles.  

Any suggestions?  I have about 250 miles on it since put this thing together and this is the first time it has acted up like this.  

[admin_JAinsworth]

The ISC is probably bad. Try unplugging it after it warms up and starts surging.

Jimmy

[BlueCuda]

Will the ISC cause problems well above idle?  I drove the car last night, it was cold 28*, I was in a hurry so I started it and drove off(gently).  It fast idled at first as usual then dropped into the idle surge.  When it is surging the idle it will not run over 2000RPM.  It just flat shuts off, tach signal doesn't miss a beat, it just kills the fuel.  Because I was in a hurry I just lugged it down the road under 2000RPM and it was fine, as soon as it got near 2000RPM it shut the fuel off.  You can floor it, it doesn't matter it wont run until it drops below 2000.  

I got my critical package delivered(my kids taekwondo belt lol) just in time!  When I arrived it was still surging and the temp gauge was 1/3 of the way up.  I dropped off the item then I moved to another parking lot and just let it run.  It surged for a few minutes then idled perfect.  Temp gauge was just under halfway, and now that it idled fine, it also ran just fine.  I enjoyed the extra power from the 20* air and gave it hell on the way home and all was good.  

So this weekend I plan to change the ISC and do the ISC TPS reset.  Is there anything else that could cause this?  It just started it on saturday, the only work that has been done on the car is different wheels, new tires, packed wheel bearings, and a few new wheel studs.  I am reasonably confident none of that caused this haha.  

[Caliber308]

In my experience with a idle that surges up and down it is most likely a ISC that is out of adjustment. There is a excellent write up here:

FAQ/HOW TO section: TPS/ISC Reset (87-89) posted by KO.

Your problem at 2000 rpms with a lack of fuel could be a secondary injector or a fuel pump on its way out or clogged fuel filters.

If at around 2000 to 2500 rpms, does the car act like it surges back and forth so much you think it is going to throw you through the windshield?

If so, it is most likely a fuel pump on its way out.

A good way to find out is to tape a Fuel Pressure Gauge to the windshield and look at FP at 2000 to 2500 rpms.

Bill

[obsolete]

Do you have a wideband AFR gauge on the car? If so, what's it reading?

[BlueCuda]

Goes full lean when the fuel drops as you would imagine.  This isn't like a starvation it is a shut on shut off feel.  As soon as the surge goes away the problem stops and the car performs perfectly.  

Cold start high idle=drives normal

Mildly warmed up idle surge starts=car will not drive over 2000RPM

Fully warm no idle surge=Runs like a champ!

I am going to dig into that area this weekend, I have some spare ISCs but first I am going to go over all the grounds, this is odd and it started out of now where.  

[obsolete]

The fact that it's fine once it's warmed up makes me think that once the ECU gets into closed loop, it's able to correct whatever the issue is by using the O2 sensor reading, and probably adding more fuel. You can verify this by hooking up an LED to the diagnostic port by the glove box. When the LED blinks, it's running in open loop (no O2 sensor feedback) and when it goes on solid, coolant temp is high enough that it's in closed loop mode and using the O2 sensor to correct the AFR.

What's the condition of the injectors in the car? Any chance the primary injector could be partially clogged? Are the injector clips/contacts in good shape? My rule for the clips is that if you don't know how old they are, just change them.

If you were able to "give it hell" on the way home, and it didn't go lean then, it seems like the secondary injector, fuel pump, and fuel pressure regulator are probably fine.

My only other thought is to test the resistance of your coolant temp sensor for the ECU and make sure its electrical connection is good. I think the expected resistance vs. temperature is in the service manual.

And of course, the other stuff that Jimmy and Bill suggested. They are a lot more experienced than me, which is a polite way of saying old! 😜

[Caliber308]

In my way of thinking, a drop in fuel amounts to where it comes from. And we all know it comes from the fuel tank through two filters and then it comes through a fuel pump to a under the hood fuel filter to the fuel pressure regulator and onto the fuel injectors and finally through two screen filters into the throttle body. Start there. The other reasons are completely different as to how much fuel if any makes it to the fuel injectors, that is electrical. Start with the simple things then work your way forward as to the other reasons as to why you are  getting no fuel or a fuel cut off.

P.S. Obsolete. Everybody gets old, even you !!!  it is what you do with your life in the short time you have on this planet to help others, that is what counts.😊

Bill

Edited February 19, 2022 by Caliber308

[BlueCuda]

Its for not a fuel supply problem, its getting turned on and off and it magically cures itself the instant the idle surge stops.  Fuel delivery is smooth and plentiful when its warmed up.  Wide open throttle it holds right around 11.5-11.0 AFR at the factory boost level.  

  I did a TPS ISC reset today, I let it sit for several hours after that and while it wasn't a true cold start I did start it with the temp gauge on the bottom.  This time it did not surge or have the fuel cut in and out deal, but like I said it wasn't a true cold start.  If I get a chance tomorrow I will take it for a drive and see if the problem is truly gone.  Not real sure why a TPS/ISC reset would cure this particular problem but these are weird cars and do weird things lol.  

What makes me feel old that is this is my second conquest, the first one I had was 22 years ago!  

 

[Caliber308]

  I  hear you. Working on the same 1987 Starion since 1989 will add years onto you😉

Bill

Edited February 20, 2022 by Caliber308
misspelling

[BlueCuda]

Cold start today, it idles higher than I think it should when could.  2100RPM, but it quickly drops down to a surge, then down to a smooth idle.  However, it is no longer doing the cut out over 2000RPM trick.  

I have another throttle body here in real nice shape.  Since it looks like the easiest way to change the ISC is to remove the throttle body I am going to rebuilt this throttle body and swap it out.  Hopefully that will take care of the surge.  

[kev]

My 88 beater has been doing this as well. When it is real cold, it’s fine. It goes to about 2K rom and then drops down. It’s when it’s warmer outside, it surges after firing up but once warm, it idles great.   I suspect the ISC as well.  Have one out on the bench to swap in but keep putting it off.   

I haven’t had it surge during driving though.  Well with exception to the old automatic transmission surging between gears at times.   That‘s my number one focus on this car, a manual conversion. 

[BlueCuda]

Ok so an update.

I have been driving the car a lot more, it has about 540 miles on it since I got it running.  Its running great but this problem is reoccurring.  I have the surge almost completely gone, it does it for a brief moment as it transitions down from cold idle to warm idle.  My company truck is being used for awhile so I am using my conquest as my daily this week.  Today the drive to work went perfect, got the little idle surge out of the way sitting at a red light and it was a perfect drive to work.  This evening it was pouring rain and I got in the car, started it and hit the highway.  That over 2000RPM cut out hit me on the highway, so I have a hard time believing it is the ISC now.  

When this happens

Tach Works

Factory boost gauge reads inline with mechanical boost gauge

Voltage is normal

AEM AFR gauge reads -- as in zero fuel.  

So something is turning the fuel off, its not going lean, the fuel is going out completely.  It cuts on and off briefly but below 2000RPM its fine.  This went on for about 1-2 miles on the highway and then it was great the rest of the way home.  This happens in the transition from cold to operating temp(mid gauge).  If I drive the car all day, if it happens it happens on the warmup.  It has to basically start from dead cold for it to happen, just a few hours and its fine.  

If I don't get sidetracked this weekend I will do the following

Change the ECU temp sensor even though it seems to OHM OK

Change the throttle body and ISC with a much nicer looking one that I have.

Double check electrical connections but this is really too predictable for a loose connection.

This could be ignition related but its not losing crank signal so I might put a new coil on it and clean up the connections but not entirely sure that will help.

 

 

 

[Caliber308]

Hook up a fuel pressure gauge and tape it to the windshield. Look at the fuel pressure at 2000 rpms. If you still have the stock fpr and  it should read somewhere between 34 to 38 psi.  On boost,  the fuel pressure and  the boost pressure  should equal appox :  42 to 46 psi. Also check the fuel pump for proper operation.

Bill

[BlueCuda]

Another 200 or so miles down.  I popped the hood today to go over some things, tighten manifold bolts for the first time since I put it back together, checked the oil, etc.  I also noticed that the temp sensor for the ECU had a broken wire inside the little boot that covered the connector.  So I repaired that and while I haven't driven it yet it already has better idle manners when cold.  I will probably need to go back in and do a TPS/ISC reset.  

Does anyone know a replacement part for the spade connectors inside the plastic clip for the ECU temp connector?  I put some regular spade connectors on for the time being but I would like to fix the correct plug if possible.  The harness from my parts car had a broken wire as well.  

[BlueCuda]

Just to update this, while I still can't verify this has fixed the fuel shutoff problem it for sure helped other things.  Now that the ECU doesn't think I am driving in Antartica it runs even better than it did before.  Imagine that? 

[Caliber308]

23 hours ago, BlueCuda said:

Another 200 or so miles down.  I popped the hood today to go over some things, tighten manifold bolts for the first time since I put it back together, checked the oil, etc.  I also noticed that the temp sensor for the ECU had a broken wire inside the little boot that covered the connector.  So I repaired that and while I haven't driven it yet it already has better idle manners when cold.  I will probably need to go back in and do a TPS/ISC reset.  

Does anyone know a replacement part for the spade connectors inside the plastic clip for the ECU temp connector?  I put some regular spade connectors on for the time being but I would like to fix the correct plug if possible.  The harness from my parts car had a broken wire as well.  

Good luck finding a stock replacement connector. If you still have the rubber cover, just use it to cover the two spade connectors, What I found that works is a old coil wire rubber cover.

Bill

[BlueCuda]

3 hours ago, Caliber308 said:

Good luck finding a stock replacement connector. If you still have the rubber cover, just use it to cover the two spade connectors, What I found that works is a old coil wire rubber cover.

Bill

I am going to post some pictures in a wiring group I am in on Facebook, its amazing the stuff people identify from OEM stuff there.  The connector housing is great, but I would need new connectors inside of it to re use it of course.  great idea on the coil wire end to cover up the spades!  

[BlueCuda]

Back on this, it hasn't cut out lately but it may not be cold enough for it to show that behavior until the fall.  I got my work truck back so the conquest is off of daily duty.

I changed the whole throttle body assembly but reused my injectors.  I had another nice looking throttle body from another engine that I swapped on.  I did a coolant flush today so I went ahead and did that while I had the coolant out.  I also made a block off plate for the EGR valve but the EGR is actually plugged where the head and intake meet.  

I did the full TPS/ISC reset minus one part, during that it says to ground a yellow/red wire.  I didn't see a yellow and red wire on the ISC so I didn't, but the rest of the process went well.  Is that wire supposed to be on the MPS connector or ISC motor?  I am also not great with colors so I will probably have my kid come out and look for me today.

Everything seems fine except it is somewhat slow to return to idle at lower speeds.  It will settle down and idle nicely at 900 but it takes it a little time to get there.  It also hangs the RPM on the shifts a little bit at low speeds.  When you are traveling down the road faster it returns to idle normally when the clutch is pushed it and the revs don't hang at all. 

Does the vehicle speed sensor have anything to do with this? My cruise control doesn't work either but I haven't bother checking into that much besides verifying the vacuum pump works.   

One other thing related to vehicle speed.  When I first swapped the throttle body I did not do a TPS reset.  It fired up and idled right and did for a long time while I was finishing up the coolant flush and picking up tools.  AS SOON AS I moved the car, we are talking less than 5 feet it started to surge the idle.  It idled for at least 30 minutes, fully warmed up, and when the car rolled back 5 feet the idle change totally with no throttle input.  

Other than these little quirks it still runs great.  The warmer air sure does rob it of some power, I was starting to be OK with it staying stock haha.  

[GoldStar]

2 hours ago, BlueCuda said:

I did the full TPS/ISC reset minus one part, during that it says to ground a yellow/red wire.  I didn't see a yellow and red wire on the ISC so I didn't, but the rest of the process went well.  Is that wire supposed to be on the MPS connector or ISC motor?  I am also not great with colors so I will probably have my kid come out and look for me today.

It's the connector for the ISC motor, but the wire you're looking to jump is on the male connector to the harness side, not the female connector going to the motor. The wire colors change over this connector. Keep in mind, that step is meant to trick the ECU to think the tip switch is closed.

[BlueCuda]

1 hour ago, GoldStar said:

It's the connector for the ISC motor, but the wire you're looking to jump is on the male connector to the harness side, not the female connector going to the motor. The wire colors change over this connector. Keep in mind, that step is meant to trick the ECU to think the tip switch is closed.

Yes that makes sense, I will do the process again today if I get the chance.  

[BlueCuda]

Did it again today, seems to have taken care of the problem.  I didn't get a chance to test drive very far but so far so good.  

[BlueCuda]

So ever since the ISC swap it never has done the cut out problem.  I have about 1100 miles on it now since I got it running at the first of the year.  If I didn't have a company truck it would be my daily driver.