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You've already described a number of physical and visual issues with fuel delivery. That would be my focus. Completely flush the system. Put some fuel additive into a few gallons of fresh gas, and jumper your fuel pump relay and let her run for a while. Drain tank (through cheesecloth if you can to inspect what comes out.) Then, with as much time and $ you've invested, I'd just go ahead and replace the fuel pump and filter (again).
Let us know more on your efforts....and more pics!
-Jason
Well, at least it runs like crap ALL the time now.
I pulled the fuel line loose from both ends (Just before the damper at the front, and just after the fuel filter at the back) and cleaned the line out with carb cleaner and air. A very small amount of the brown gunk came out. Maybe 1/4 tsp. Not at all the milkshake of death that came out of the filter. FYI, when I had the fuel rails out, they were totally clean inside. I put some fuel system cleaner in the tank and ran the fuel pump for a while. I didn't replace the filter and pump again...but I'm not at all convinced they're a problem now. The fuel is coming out nice and clean, good flow. Definitely enough fuel quantity for the engine to idle.
Since changing the injectors and fuel filter, the problem has gotten a lot more consistent. It was all over the board before, up and down and random. Now, it's quite predictable.
If I start the engine and let it run without touching the throttle: The engine will run fairly okay for about a minute, then the idle speed will slowly start to move up and down. The surging will gradually get stronger and stronger. After a minute or two of running, this idle speed dip/surge becomes severe. Idle speed will dip down near death, then you hear the ISV open up, suck air and over-correct, and the RPMs surge up well over 1000. Then, it goes back down near death, and over 1000, repeatedly roughly every 3 seconds or so. Eventually, during one of these cycles, the ISV will open up, but just a little too late and the engine will die. It will start right back up after that, but will continue cycling up and down and die within 10-30 seconds or so.
Now, that's what happens if you don't touch the throttle, and you just let it be.
If you open the throttle just a bit, (just enough to open the throttle position switch off idle, perhaps?) then it will usually go up to around 1000 RPM and you can get it to stay running there. From there:
- If you release the throttle: It will just flat _die_. Immediately, like you turned off the key.
- If you open the throttle a little tiny bit: Like enough to get it up to 1150 RPM. It runs rough, but will slowly move the car. Once it's moving, you can give it just a tiny bit more, like add another 100 RPM. You can gradually get it up to freeway speeds this way. Drivers behind you are visibly angry. You're worried about the cost of bodywork to repair all the dings from other drivers throwing objects at you, but it will get you to the grocery store.
- If you open the throttle enough to drive like a normal person: It coughs and sputters and even pops a little bit out of the exhaust. Absolutely no power. It will, after about 7-10 seconds, sort itself out a bit and go, with much hesitation.
Often, you can fully release the throttle for 1/2 second or so, then open it back up to the "drive like a normal person" position, and the car takes off enough to make it up the hill or whatever. Still very rough running. No giant BANGs like a huge rich-mixture problem, just occasional little pops. Also, I'm not seeing any sooty exhaust or rotten-egg smelly catalyst or anything that leads me to believe it's severely rich.
Next time I get a chance, I'm going to check the O2 sensor output. I suspect maybe it's really sluggish, and the cycle of die/surge behavior is happening every time the O2 sensor switches. I'll probably recheck all the sensors from the LH/EZK connectors while I'm down there.
Also, someone has popped the cover off the adjustment screw on the MAF- no telling if that's adjusted correctly. I have an ancient exhaust gas meter that I think I can use to confirm that.
You should check out @Michael Benno 's thread on his high idle issue. He posted a video that looks like exactly what you describe above, when you don't touch the throttle.
Just a thought, if you haven't checked for air leaks.
What you're describing in terms of running symptoms with throttle application sounds like limp-home mode (no MAF signal), with a fixed injector pulse width which is just enough for slightly above idle speed and low load (get to the side of the road - not home).
The candidates I'd identify based on your symptoms are:
1. MAF issue (they degrade with age - voltage output drops until they're ignored - the potentiometer in them is not connected electrically on your car so don't worry about the cap thing)
2. O2 sensor / loop issue (check the connectors and for frayed wires on the way to the sensor)
For testing item 1 - Simplest test - if you unplug the MAF, does the engine behave the same? If it behaves the same without it connected, your MAF is an ornament and needs a rebuild.
Inspecting item 2 is relatively easy.
If still not conclusive, then from where you're at now, I'd be seeing if there's a friendly local owner you can try a MAF swap and LH swap (not at the same time - isolate the problem) before you end up throwing a bunch of money as a shot in the dark.
Latest update:
I replaced the O2 sensor yesterday. Didn't bother testing it first, but it must have been pretty bad because changing it made a big difference. The car is running very consistently now. Extremely noticeable improvement at higher RPMs, but still dying and surging at zero throttle.
The exhaust flange nuts were miserable. Two came off with PB Blaster and a breaker bar. Another two came off with PB Blaster, a breaker bar, and a 1/2" impact gun. The last two rounded off completely after PB Blaster, a breaker bar, an impact gun, and a torch. They had to be cut off with an angle grinder and a chisel.
Word to anyone else that reads this: BUY NEW NUTS AND BOLTS before you take the flanges loose. You'll need them!
I'll take a look at that video from Michael Benno. Do you know which thread it is? I'm having trouble finding it. EDIT: I found it here, and YES, that's almost exactly what it's doing!
I'll try unplugging the MAF and see what it does!
Last edited by android606; 04-10-2023 at 10:32 PM.
Hi Andrew, in that video I posted, I had been driving the car for about 20min when that started happening. I am not really sure why the car was doing that. A possible overreaction to too much air getting around the throttle plate and the ISV/ECU trying to counteract the dying. My car has a high idle that is stemming from too much air getting around the throttle plate. But this same problem could be caused by too much outside air getting into your system as well.
The fluctuation we are both experiencing is a result of the ISV acting slower than the influence of the air leak, and thus it overcorrects high, then low, and after a few cycles, the idle gets too low and dies. This is a good sign that your ISV system is working. And, a sign that something else is wrong.
For troubleshooting, the factory manuals state that it is important to follow the specific order of tests to properly identify the issue. Doing the tests out of sequence can lead to misdiagnosis (their words, not mine). For troubleshooting your car, I would strongly recommend you used this guide as your bible: WKD 493 921 - Test Plan EZK and LH '87. There are some tests that call for an oscilloscope, so that is where rennlist can help you interpret your tests and provide alternatives. In that document, there is a handy chart that identifies symptoms and tests required. In your case "Irregular Idle".
Side Note: I have created a spreadsheet of that chart, that allows you to filter to the specific symtom(s) you have and see the tests to be conducted, as well as, the corresponding pages in the WSM. I would recommend you make a copy of this file for your own personal use: LH and EZK Diagnostic Grid
Opinion and Observations: In reading your thread, an internal air leak internal or external would be high on my list of things to check. It might be helpful if you were to post a list of the parts replaced in the intake, that will help rule out some components.
Last edited by Michael Benno; 04-11-2023 at 06:49 PM.
Hi, @Michael Benno Thanks for the input and the fantastic spreadsheet!
I've been trying to follow the procedures in the WSM, but it's hard to do all of the tests in the correct order without a "Hammer" or an oscilloscope. Plus, this is a severely neglected car. I mean, it had a rat's nest in the intake. It has definitely had multiple problems coexisting- not the kind of situation the neat procedure in the WSM accounts for.
I did some really lazy checking for intake leaks, but that was months ago now. The engine was running really badly and unpredictably back then, and it would have been hard to tell if anything I was squirting around the intake was actually making any difference.
I've replaced several parts since then- Fuel pump & filter, Injectors, O2 sensor, Temp II Sensor, and very carefully cleaned up the MAF. Every one of those things made a noticeable difference.
I believe pretty much every "wear item" under the intake has been replaced: Knock sensors, hoses and clamps, gaskets, etc. The throttle position switch is original, but it's definitely working. The ISV sounds to me like it might be slightly sticky, but it is working.
I think my next steps will involve testing the MAF, and doing a much more comprehensive leak test on the intake. I'll probably pick up a smoke tester like yours. While I'm at it, I'll try filling out that spreadsheet, too.
I haven't wanted to think it after paying $4k for an intake refresh, but it seems likely I've got a false air problem on my hands.
It sounds like you have done a lot of good troubleshooting and replaced some key parts.
Since you mentioned a rat problem, I would strongly recommend you inspect and test your wiring connections for rodent damage. In my experience mice and rats will often chew on the insulation of wires. In particular, inspect the harness to the EZK and LH from inside the car to the sensors. One thing for you to verifiy with the service tech that worked on your car is to see if that adjusted the throttle plate stop or adjusted the throttle plate itself. If so that could be a clue.
MAF testing, you can send your MAF to http://www.injectionlabs.com/ for free testing and they will tell you if your MAF is out of calibration. It will take about a week. Some of our site sponsors who do MAF exchanges may also do testing so use them as well. My understanding is that unless your BAF has been rebuilt it WILL drift out of tolerance. The rebuild process replaces a component inside the MAF control that does not drift, and in some cases, they will replace the platinum wire.
Sticky ISV, can definitively cause the issues you describe. The way the ISV works is based on voltage. The LH applies more voltage to get it to open more. If it is sticking the LH will continue to apply more and more until the ISV breaks through sticking point with too much voltage then the ISV is too far open then it has to close some and if it is sticking in the closing sweep you have the same problem. On top of that the ISV response is lagging in comparison to what the engine needs at any given moment (as compared to FI response to. MAF or O2). Subsequently the a sticking ISV is definitively a problem and you should spend some time digging it out and doing a thorough cleaning with PB blaster and probably test it if you have a variable DC power supply. For reference, in my troubleshooting the intake can be removed in about an hour (with practice) and re-assembled in about 3hrs including fuel connection tests.
Testing for air leaks in the Intake: There are several methods to test each with different pros and cons. When testing the intake remember the intake vacuum system is connected to both the crankcase breather system and the brake booster system (booster, Cruise, HVAC, and Flappy). I'd recommend you disconnect the booster system and test that separately (see below) to help narrow down the possibilities. Disconnect the large vaccum line to the booster and put a plug in it, or use that line as your access point for the tests below. When testing the intake you need to plug all the holes. The big one is the plugging the MAF you can build your own MAF Plug pressure tester, Our use a thick plastic bag between the MAF and the throttle boot to seal the MAF hole. I use the later method when smoke testing so I don't contaminate my MAF wire with oil vapor from the smoke machine.
Pressure Testing - plug all the holes and use a compressor with a pressure gauge. You are looking to hold about 1PSI or more and it will drain to zero over the course of a minute or so. This will help you identify how air tight your intake/crankcase breather systems are, but will not help you identify where the leaks are. But the benefit is you likely already have the tools to do it. There is inevitable leaking down is coming from the valve seats through the cylinders.
Smoke Testing - same as above, but the smoke helps you pinpoint where the leak is, let it run for 15-min or so. Validate smoke has filled the intake by unplugging one of the vacuum line to the front fuel damper. This test is good but lower pressure than the pressure test, unless you can increase the pressure on your smoke machine to more that a few psi.
Vacuum Testing - in some cases you may have a leak that is only apparent under vacuum vs pressure. This test will require a vacuum pump or can be done with the car running and a propane torch. Use the torch unlit to disribute propane around possible vacuum leak areas (eg injector seats) and notice when idle changes.
Regarding rats and wiring: Yes, the air cleaner was full of one rat's nest, and the valley under the intake was another rat's nest. The wires leading to the knock sensors were in hilarously bad condition. They were too crusty to even tell if they were chewed up or just rotten. The ISV and TPS wires were filthy but intact. I've deliberately been testing my sensors and switches at the LH/EZK connectors so as to ferret out (ha) any wiring problems.
My smoke tester arrives today. It has a ~1psi pressure regulator and also a flow gauge, so even if no obvious smoke pours out anywhere, it still might be a useful pressure test.
Unfortunately, I probably won't have time over the next week to play with it. I have urgent house repairs to attend to. I'll be back after I do, though!
I know this isn't a Porsche, but here, take a look at this weird car I saw while I was in Massachusetts picking up the 928:
Smarter minds than mine are already working on your more serious issues, but there are a few bullet points I have experience with:
Roger (928sRUs) sells a replacement washer fluid reservoir neck that is an improvement on the stock design. If your current one is broken and crumbling, there's a good chance the reservoir is a cesspool of rust and plastic. Take the wheel well off and give it a good wash-out. While the wheel well cover is off, check the Y connection to the charcoal canister
If you're adding a small subwoofer anyway, it might be worth disconnecting the rear speakers entirely and just getting a nice new set of components up front. Some models have about 5 times as many speakers as our cubic footage can reasonably contain. Unless you're going to get a really high end DSP setup, the rear speakers interfere more than they assist.
Here and here are two really impressive dash recovery threads
@LargeFarva Thanks for the tips! I'll definitely check out the connections in the wheel well. I might just replace the hoses in there whether they're leaking or not. Small hoses are cheap. The entire washer fluid system is toast. All of the nozzles are broken or missing, almost all of the hoses have crumbled apart, only one of the pumps makes any sound when you press the button, and I haven't dared to try putting actual fluid in it yet. Once I get this engine problem under control, I'll dig into that, and definitely hit up Roger for that filler neck upgrade!
The speakers might have been acceptable by 1987 standards, but to my ears they're truly awful. It's been my experience that any mid-grade head unit with more than 30 watts (not counting the sub) can make as much clear sound as I ever want, if they're driving a set of decent speakers. I like music, but I don't think I'm too hard to please. Do you have any specific speaker models you can recommend that fit up front and sound okay?
Speaker fitment is a tricky proposal as almost no one makes tweeters that match the size of the factory mounting location. I'm still trying to answer that question for my current project. Someone on eBay sells 3d printed reducer rings but it's not what I'd call an elegant solution:
I have a set of Alpine R-S65 components that I'll be testing out, but my door panels were already cut by a previous owner so I don't know if the depth will work unmodified
03-25-2023, 11:54 AM
