OK, before somebody tells me to look for a vacuum leak...been there, done that, all lines replaced, except brake booster line, but it is also OK. Also the vacuum lines to the fuel vapor canister, also switched them around, just in case the PO had messed with it..........no change. TV cable is also adjusted right. Let me list what I have replaced after checking for vacuum leaks.
EGR MAP MAT O2 sensor IAC TPS CTS PCV Injector TB gasket ECM Oli & filter Ground cables
Still hunting when warm/hot. Sometimes also stalls. Runs great when cold.
Here my question; can a faulty oil pressure switch cause idle problems? I know the fuel pump relies on information from the OPS.....and I also know that I accidentally shorted the OPS a while back, trying to connect it correctly again (someone from the Georgia Fiero Club told me I probably blew the fuel pump fuse, which was dead-on!), because the PO hacked around on the cables (only 1 cable connected to the OPS). I'm suspecting that something has been wrong with the OPS from the beginning. The PO also installed an 87 OPS instead of an 88 OPS, which I have, plus the 88 connector. So while watching my instruments, I notice the fuel pressure takes a dip, then right after that, my idle takes a dip. It almost sounds like not enough fuel when the idle dips. Does what I am explaining here make sense? Could it be related? If the moon is in the seventh house and the wind is blowing just right?
Frustrated in Germany...........Don
[This message has been edited by Donster (edited 03-13-2019).]
There's a common misconception that the OPS acts as a fuel pump cut-off switch. It does not. It's actually a back-up for the fuel pump relay. If the relay is working properly, then the OPS will have no affect on fuel pump operation. The only exception would be if the OPS switch sticks in the ON position, causing the fuel pump to run continuously.
You said that you checked the brake booster line. But did you pinch it closed, to make sure the booster itself isn't leaking?
Also, I don't see any mention of the O2 sensor. When the engine warms up, the O2 sensor comes online. That's a possible culprit.
Had this issue in a 2.8 V6. Timing was just not done right. 10° off, it runs great cold. Idle wants to hunt when warm. In my case, I had the distributor O-ring replaced and we painstakingly marked the distributor. The ringer was that the oil pump driveshaft came out with the distributor. In hindsight, we lined our marks up, but probably missed a tooth on the distributor/cam gear. Not certain of 4cyl timing procedures, but it's worth ruling out.
I think I have narrowed it down to the IAC. Seems that I got a bad one out of the box. Will test with IAC procedures from here on the forum and update tomorrow.
Iffy power/grounds will cause hunting idle. Alt brackets are ground for the alt. Crap Wires to alt or battery or "block" under C500 and others can cause this.
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
But I've checked ALL cables, positive AND negative/ground and they seem OK. Ones that were questionable I replaced, but symptoms persist. Could a bad exhaust also be the cause? Not enough back-pressure?
I tried resetting the IAC valve using the procedures I found here on the forum and in the manual. But after taking it out of diagnostic mode with the IAC unplugged, the engine will not start, so I cannot adjust the idle air screw. Is this an indication of a bad IAC? If I plug the IAC back in, engine starts again, but of course with the symptoms again once it runs warm???
Originally posted by Donster: I tried resetting the IAC valve using the procedures I found here on the forum and in the manual. But after taking it out of diagnostic mode with the IAC unplugged, the engine will not start, so I cannot adjust the idle air screw. Is this an indication of a bad IAC?
I tried it again, but with the IAC disconnected, I cannot get the engine to run. I'd hate to screw with the screw (no pun intended), as I have read so much negative about it here. Since nobody here told me if that was an indication of a bad IAC, I have ordered a new one, which should be here in Germany by Friday. Guess I'll soon know. :-)
Static idle is "sealed" for good reason to stop ID10T from F'ing up this. Not just GM but Ford Chrysler and other to meet Fed and often State Rules. But... If the Seal is gone then you need to check because many think adjusting this "fixed" whatever problem and most only make more problems.
Even if the Seal is intact... Idle stop screw and point it hits and throttle pivot points can wear. Just how bad depends on many things and you may need to adjust idle for old cars. If really worn then may need a newer TB TBI or Carb. GM cars are often better for this but still can happen. One of worse was first version of Chrysler Mini Vans w/ 4 cyl that had a very thin screw tip that could literally hammer a hole thru the steel stop and completely close the throttle.
All Fiero engines covered here from GM FSM, See my Cave, Idle Stop
Note that this problem Will Not cause Hunting Idle for most cars. Crap power/grounds will and a few others. Just 1 iffy ground in the cabin or engine bay can cause this. Common grounds etc See my Cave, Wire Service Don't just look at or even "test" grounds and power block under C500. Take apart all ends, clean and lube w/ silicon or brake grease at minimum. Either grease won't wash out easy and won't eat plastics.
Thanks Ogre! The articles in your cave will certainly help me hunt down any possible bad grounds or connections. Very informative....and your knowledge is amazing!
But perhaps you can answer this for me: If my hunting idle when warm is due to a bad or iffy ground, would this problem not also be when the engine is cold, not only when warm or hot? Or is the circuitry in closed loop so dominant that it maintains a steady idle and only becomes evident once the ECM takes over?
I am still hoping that the IAC is the culprit, but will tear into my wires this weekend using your information. Thanks again,
\D
[This message has been edited by Donster (edited 03-20-2019).]
Don, I don't know if the L4 IAC is the same or designed the same as the V6 IAC, but how are you adjusting it before installing the new one? The V6 has two style IAC's and their method of adjustment differs.
One has a smooth, round pintle shaft. That one can be screwed in to set the initial adjustment of 1 1/8 inch. The other has a slotted shaft and if it's twisted, it will destroy it. For the smooth shaft, retract the spring from the pintle head and turn the pintle head. For the slotted style, place your thumb on the end of the pintle, exert pressure and rock it side to side. The initial setting should be just a hair less than 1 1/8 inch from the tip of the pintle to the surface where the gasket rests on the body of the IAC. If the IAC is installed with the pintle extended more than 1 1/8 inch, it can be damaged.
The V6 IAC is threaded to screw in. The L4 IAC needs to be fastened with 2 screws. They are quite different. The last one (out of the box) had the pintle screwed all the way in. I hope the new one is the same way. Once it arrives and I install it I jumper pins A & B (diagnostic mode) with key on, engine off, wait 45 seconds or more, then I disconnect the IAC, take it out of diagnostic mode and that is when I would start the engine and try to adjust the idle air screw. After that, I re-connect the IAC, and start up the engine. Optionally, I disconnect the ECM and re-connect it before driving at least 35 mph or more for about 20 or 30 miles, applying STOP & GO and also shutting off the engine a few times. As they say: By the book!
It is quite different. anyway, look at the pintle shaft. I'm sure the same methods of retraction would be required before installing if the pintle is extended too far.
Close loop happens after ECM sees a good signal from O2 sensor. As little as 30 sec after start. O2 sensor Is Not a "one wire" but looks like it because O2 ground is bolted to the trans bell bolts.
ECM knows volts and iffy wires can lie to ECM for this and most anything else.
other iffy wires can cause a lot of headaches including Hunting idle
Had the time to go through all my wires again, couldn't find any that looked iffy. Took out the entire C500 and redid the wires. Still waiting on new IAC and still idles like crap. :-(
...after taking it out of diagnostic mode with the IAC unplugged, the engine will not start... If I plug the IAC back in, engine starts again, but of course with the symptoms again once it runs warm.
I'm curious... what happens if you simply unplug the IAC while the engine is running? Does the idle continue to hunt?
Hmmm... I'm surprised. I had an idle hunting problem with a '94 Hyundai Elantra, and my solution (although inelegant) was to simply unplug the IAC while the engine was running (and at the low end of the hunting idle RPM range). Solved the problem. No trouble codes generated... and the engine continued to start, run and idle just fine. It's too bad a procedure this simple apparently won't work with an '88 duke.
[This message has been edited by Patrick (edited 03-28-2019).]
Rebuilt TBI with new gaskets, O-rings and everything else, still hunting idle. The only thing I have not yet replaced are the 2 ignition coils. Could they be at fault??
So, does anybody think it could be the coils? I've replaced so much, it really wouldn't matter to me if I need to replace the 2 coils, I just want to know if they could be the problem before I replace them, as it is rather difficult to get to them.
Ignition is Not likely for this problem. See my Cave, DIS Ignition
You didn't scan the ECM all this time? Should done this First. Example: ECM reads Volts etc to ECM and will cause problems when ECM sees low or high volts often not setting "Codes." Crap wiring in a lot places can cause this problem even tho Alt putouts ~14.6 volts. ECM can be "dying" or any wires to it can be crap. Some sensors should read relatively constant while others charge every scan. See my Cave, Scan Tool Help and rest of section. reddevil has scan tool works w/ 87-88 duke.
Perhaps you can point me in the direction of possible bad wires/ground? Or are there too many? I've taken apart the C500 next to the battery and redone all of the wires. Wich are the ground wires that could have such an effect on the idle?
I ordered a scan and diagnostic kit for the 87-88 Duke yesterday, what exactly, when I scan, should I look for?
As always, your input and suggestions are much appreciated!
ECM read cave section. Example: ECM should see and post to scan tool same or very close to same Volts as Volts measured at battery AND alt output terminal and red wire to alt's side plug. IOW Alt should be ~ 14.6v when running then ECM should see and report ~ same. If ECM see < than that like under 13.6v or worse 12v then have a major wiring problem(s) causing low volt. Worse, Same problem is likely cause low volts to a lot of other things including fan motor, heat blower, etc, covered in Electric Motors that can kill them too.
Even if they match... Start check/clean/fix all grounds listed in cave. Take all apart not just look at the ends. If rusty or painted clean to bare metal and coat the metal w/ brake/silicone grease. Don't over tighten and break things because grease make that easy.
Then do same for battery cables and alt output wires etc. Better to just replace battery cables w/ ACDelco parts, not aftermarket cables w/ lead battery ends. Coat w/ brake/silicone grease. Use small 5/16" wrench and tighten just enough to deform the lead on battery and hold. Doesn't need much to "strip" the battery nuts inside the holes. Many fools wreck the battery using bigger wrenches. Big reason Why many sell "battery wrenches" just for this job.
Another example: If alt's mounting hardware is iffy... The hardware IS ground for the Alt. Crap hardware = Crap ground and often can see measure volts output to case then output to engine. Common to loose 1v or more just for crappy alt hardware. Then when you have other iffy ground and/or + side you can drop 2 or move Volts to any or all of car. What More Fun? Try turning on HeadLights w/ engine running. Measure Volts alt output to case then output to frame then in front @ HL socket black wire to whatever wire is have power. (Leave socket on the bulb to measure. you need both bulbs amps load to see this better.) I bet HL is 1 - 4v or more lower then back because likely have crap grounds in front and problems w/ HL main and/or dimmer Switches at minimum. 1v drop often won't matter and won't see dim light but higher V drop then likely will see dim lights and heat up the dimmer and/or main switches because they wear out and get more resistance.
Scanner / diagnostic kit has not arrived yet, but...........today I had the exhaust out to repair it (long story) and I noticed that from underneath, you can see a bracket from the alternator to the TBI. It was completely rusted and once I looked at it closer, I noticed the screw going into the TBI is torn off, hence, no real connection there. I remember the Ogre mentioning that the bracket itself functions as ground. Is it this one?? Could this be my issue??
Tore apart center console today, checked all ECM cables there, sanded down ground connector, used a stainless steel screw. Went at the C500 connector again, replaced positive cable from battery to underneath C500 block, replaced negative cable to engine, replaced ground cable from engine to chassis, sanded all surfaces. No change, idle still hunting. Scanner / diagnostic kit won't arrive until sometime next week. Had fun troubleshooting in the beginning, sort of a challenge. Now frustration is setting in.
[This message has been edited by Donster (edited 04-07-2019).]
Put in a RD belt tensioner 2 months ago..... All alt grounds replaced.......but........ Quick question regarding the ground connections: I have a heavy gauge wire that goes from the (-) battery to the engine block (good shape). Then I have one that goes from the engine to the decklid frame (flat copper, good shape). But shouldn't there also be one directly from the (-) battery to the body/frame?? Is it vital? I don't have that. Where would/should it be connected to the frame?
On the V6, the alternate ground comes off the negative terminal and bolts to the battery tray. Maybe the L4 is the same.
Thanks Charlie. I think they are the same. Been looking thru the forum and I kept reading about the direct ground from (-) battery to the tray/frame/body, and it seems to be V6 AND L4. Would be great if I had an 88 SM to flip thru. :-)
[This message has been edited by Donster (edited 04-09-2019).]
Did you inherit this problem from the previous owner, or did it start doing this later on? How warm does it have to get before it starts idling badly?
You mentioned replacing the injector, but have you checked if it's actually spraying okay and there's no dripping? Are you sure it's the right injector for the car? I've read you can use a timing light to see the spray pattern as it idles (never tried it myself). Warm idle is when the injector is operating at it's minimum duty cycle and that's when they're most prone to be erratic. It's also when they're the hardest for the ECM to accurately control. Warm idle is also sensitive to sensor/wiring issues for basically the same reason. Definitely review all the sensor data when you get your scanner.
Unfortunately, the issues were inherited. Injectors were both tested by Bosch Services. I had no idea that they do that here in Germany. Tested out good. I also have good fuel pressure.
OK, the more ground / earth connections I replace or clean up (stainless steel bolts & nuts, grind to bare metal), the better the car runs. Seems almost perfect now, except for a slight stutter/drop in the idle every now and then. I'm still waiting on the scanner, but I am obviously on the right track here.
As usual, I will update here every time I do something.
You adding SS hardware may not be helpful in the long run. Adding more different metals can make worse problems when polluted water get on whatever. Worse if you don't use silicone/brake grease to keep water off the metals. Even in the cabin you get enough water as condensate as wet air hits anything cool. Just google: dissimilar metal corrosion
Ogre, I DID heed your advice and used silicone / brake grease on all connections that I cleaned / replaced. The stainless steel was more for troubleshooting than anything else, as you have better connections / conductivity when first used. In essence, I was just trying to find which ones would have the most impact. They can all be replaced again eventually, with regular bolts and screws.
And I'll say it again: Your insight and recommendations were vital in hunting down the hunting idle (no pun intended). I'll update once I receive my scanner or have any changes / improvements.
Hunting idle isn't only thing fixing ground will help. Like front grounds near HL assem's effects most things in the front of car but will never set ECM codes, hunting idle, etc.
Note that you often Won't see iffy grounds and connectors w/ most Ω meters. Even 20awg wire and related connections are too heavy to see a difference using them. Often can see brighter HL bulbs by cleaning front ground and bulb sockets. Other bulbs might not see a diff unless grounds etc are really rotten. Rest often can see problem testing for voltage drop on a wire, more so w/ big amp loads say rad fan but easier just fix/clean all grounds.
Work thru ground etc in engine bay and two main ground in the cabin. While sounds weird... the Fuel pump is grounded in the cabin.
Can try removing/replacing some plugs too even if they are "water proof." Alt side plug, ECM, large one next to ECM, C500, and "Box" w/ bolts under C500 for a start. Sound dumb but Replugging connectors a couple times often cleans minor corrosion and fixes a lot of issues. This ECM more so because board edge connections sim to PCI etc in a computer but just plug connecting to solder on board edge. IOW Plugs works same as PCI but ECM doesn't have "gold fingers" like PCI does and solder will corrode over time alone. Do Not disassemble the ECM beyond cover over PROM. This can cause problem just removing main cover because is bolted to part on the board and old ECM can "die" w/o warning.
I'm going to write a book with all the tips you have given me! :-)
BTW: I was told on the GA Fiero forum, that there is a ground connection in the rear right fender well that is notorious for causing issues / bad ground. Where exactly is it located?
Remove the right rear wheel well liner. It's located on the outboard side of the upper frame rail at about 11 o'clock. It is a clip that's bolted to the frame rail with a heavy black wire.
