• Hello Guest, welcome to the initial stages of our new platform!
    You can find some additional information about where we are in the process of migrating the board and setting up our new software here

    Thank you for being a part of our community!

240 Hard Start, loping idle

simple sensor or connection could be bad.

EFI is about inputs/outputs...and checking them one by one on older EFI systems (pre OBD-1)

For instance, with a good coolant temperature sensor verified with ohm meter, warm it up to hand temperature, then on a cold morning...hook LH's electrical plug to it, ground CTS out to battery, then start engine on a cold day. A simple test....that informs LH that engine is warmer than engine's block, which decreases fuel amounts

LH's CTS increases in ohms with increasing coldness. One could measure ohms at LH's wiring harness by removing harness from its box, then measure ohms at pin.

Either LH is dumping more fuel than is needed, or an injector is pissing away, 24x7x365.
 
So no one thinks part of it is from the blown out exhaust manifold to down pipe gasket? Anyone else care to chime in? Roy, calling, Roy. I'd love to hear some knowledge from you on this issue
 
Do an ohm meter test at LH 2.4's harness plug for CTS...if within specs, this may suggest a leaking injector.
 
What you describe are classic symptoms of a bad AMM. Borrow a known good AMM and throw it on there and I'll bet every one of those issues disappears instantly.
 
I understand that. But it may not be mechanical. This vehicle is old enough that a simple sensor or connection could be bad. In a perfect world I would have this fixed by the time I leave for NTC next weekend

If the cold start injector is stuck open, unplugging it will not change anything.

So no one thinks part of it is from the blown out exhaust manifold to down pipe gasket? Anyone else care to chime in? Roy, calling, Roy. I'd love to hear some knowledge from you on this issue

No, it has nothing to do with the exhaust gasket. If the exhaust leak was causing a bad o2 signal it would also act up when warm.

One thing I have not seen is, Is the check engine light on? What codes does the ecu throw?
 
What you describe are classic symptoms of a bad AMM. Borrow a known good AMM and throw it on there and I'll bet every one of those issues disappears instantly.

That is what I was told when I bought my car, turned out to be a vacuum leak in the line going to dash the vents.
OP: you cant just inspect the lines, you gotta pull them off and re-install them. More than once I have found hardened lines that are not sealing to the nipples anymore, but are not cracked or split. Or they split when removing them. If they come off easy with a pull, they are likely leaking. Over the years I have found quite a few bad lines this way that I didn't see when inspecting them visually.
Did you check the lines that go to the charcoal/vapour can?
 
That is what I was told when I bought my car, turned out to be a vacuum leak in the line going to dash the vents.
OP: you cant just inspect the lines, you gotta pull them off and re-install them. More than once I have found hardened lines that are not sealing to the nipples anymore, but are not cracked or split. Or they split when removing them. If they come off easy with a pull, they are likely leaking. Over the years I have found quite a few bad lines this way that I didn't see when inspecting them visually.
Did you check the lines that go to the charcoal/vapour can?

I guess you missed the part about the intermittent flat spot in the power band. Think. Does a vacuum leak come and go? There are too many indicators it is the AMM. A vacuum leak would still be leaking when the car is warmed up, yet, the surging idle goes away. Another classic failing AMM symptom.
 
I guess you missed the part about the intermittent flat spot in the power band. Think. Does a vacuum leak come and go? There are too many indicators it is the AMM. A vacuum leak would still be leaking when the car is warmed up, yet, the surging idle goes away. Another classic failing AMM symptom.

I guess I didnt express myself correct, I didnt intend to say that in this case it is not the amm.
I did want to express that old bad vacuum lines have a nasty way of hiding their issues, and causing symptoms seemingly unrelated. Visual inspection is not enough.

One thing I have not seen is, Is the check engine light on? What codes does the ecu throw?
There should be codes if the engine is acting up like this. People are talking about ecu swaps, but not about if and what codes are being thrown by current one.
 
That’s the one thing OBD 1 does not detect, a failing AMM. If the hot wire is broken, or, the AMM is unplugged a code is thrown. All kinds of running issues do not trigger any codes when caused by the AMM. Sometimes, the code for too lean/rich is triggered by a bad AMM.
 
Last edited:
Thanks for pitching in Roy! I understand unplugging it won't fix anything if its stuck open, but if its possibly a dying ECM, that could trigger it if it isn't. When i get back from the **** hole known as NTC, that CSI is going bye bye. Hopefully I can get around to double checking injectors sometime between now and Thursday night. I for whatever reason cannot find my Haynes book right now. What would the specs be on the ECT and the injectors?
Ok. To recap:
-No CEL, no codes pulled, 111.
-The ECM ECT was replaced in 2016
-Cap, rotor and plugs were replaced last IPD Garage Sale
-Vacuum lines were replaced last summer when the problem first started to rear it's ugly head
-Swapped AMM from my 91, no change in start up or driveability
-FPR, intake and exhaust mani gaskets were replaced when the ECT was(back in 2016)
-Inspected intake accordion and found no splits, cracks or holes. All good.
 
That?s the one thing OBD 1 does not detect, a failing AMM. If the hot wire is broken, or, the AMM is unplugged a code is thrown. All kinds of running issues do not trigger any codes when caused by the AMM. Sometimes, the code for too lean/rich is triggered by a bad AMM.

Prev Owner of my car sold it (amongst other reasons) because it was throwing the lean rich code occasionally, along with other running symptoms, and for all the world looked like a failing amm. If I am correct, according to him, He changed (more than once) it for the chinese re-pops and they failed fast, then he tried to get a reman bosch from ipd but they were out, refunded him and he couldn't find another good one.
I found/fixed vacuum problems and all symptoms went away. One was the dash vacuum hose that was uncracked but hard and leaking around the fitting. This vacuum leak varied depending on what the dash vents were set to, due to an additional leak under dash. The other was a cracked flame trap housing. Oh, there was also a check valve installed backwards.
 
Yeah, I knew there were different sensors made by Bosch. For the life of me, I couldn't remember the webpage that had that info, thank you 84B23F.
 
Idle Air Control (IAC) valve? When mine was going out it would stall at idle since it wasn't doing what it was supposed to. A very easy fix to R&R.
 
Maybe I can try guess and check with my 91 ECU? I didn't even pay attention to which ECU is in the car when I replaced the expansion valve when I got her AC working two years ago. LOL Non-the-less, I shall double check the ECT.
 
Just swap ECUs and see what happens. It's really the EZK that controls EGR anyway. If that seems to make a difference, swap your 1990 ECU into the 91 and see if the symptoms follow it. 15A discovered over the weekend that the running issue he has been chasing on his 1993 940 Turbo was likely the ECU. He swapped in a later version, known good ECU and suddenly the intermittent miss went away. He has had the issue with that car for 3-4 years.
 
Just swap ECUs and see what happens. It's really the EZK that controls EGR anyway. If that seems to make a difference, swap your 1990 ECU into the 91 and see if the symptoms follow it. 15A discovered over the weekend that the running issue he has been chasing on his 1993 940 Turbo was likely the ECU. He swapped in a later version, known good ECU and suddenly the intermittent miss went away. He has had the issue with that car for 3-4 years.

Gross. Yeah. It started out as a rough cold start about four, five years ago, now it's a really rough start, and a PITA to start when the ambient temps are below 50 or so.
 
Back
Top