Very erratic cold idle. Is this an ECU issue?

[Sailbad_The_Sinner]

Hi gents,

My '91 Fed. spec. surges and almost dies, and sometimes does die, at cold idle, but once I go a few blocks it smooths out and runs great. I'm sure this subject has been covered to death here but it's easier to do the lazy thing and let y'all spoon feed me. Other than a prodigious oil leak, where the head meets the block at the right-front corner (I think) this is my only remaining issue to be addressed.

Should I replace the ECU or what? Thanks in advance from the great but very soggy (and sad) State of Texas...

Dave

[chrism]

Hi Sailbad, I'm by no means an expert but my first thought might be a duff temp sensor, perhaps also an O2 sensor. ElanScan might narrow it down further if you have access.

I, too, had some seeping from along the front cyl head area - and the odd drip from the lowest point of the engine. Thinking that it could be the dreaded head gasket, I'd read that the camshaft oil seals / o-rings often get hard and worn so I took the 'easiest' (rear) out to measure up a couple at my local accessory shop. He only had one so I took that and fitted it all back together with the new one. Luck of the draw; it totally cured the leak.

It costed £0-45p but a bit of a beeaatcch to get at! The other one is exactly the same seal - but under the Cam Angle Sensor

[Fredjohn]

I would tend to agree with Chrism on both counts. Always check sensors before blaming ECU!
And sensors are the cheaper repair.

PS realise you have a FED car, but adding your location, even approximate, often helps in solving problems.

[Tuga2112]

i dont recall ever hearing about an Elan ECU failure. that obviously wouldn't rule out your situation being the first.

but as others said. the coolant temp sensor is the first thing to look at. (and i can tell you in the past 2 years, there has been at least 4 reported failures i've witnessed.. making me assume the factory ones are probably now reaching their designed EOL)

I think o2 is not likely because they actually only operate after they warm up, and you describe the issue to be on cold engine. which I assume means, "its problem as soon as you start the car".

one thing to cxonsider is to start car in diagnostics mode.
according to what i read (although i am not 100% convinced this is factually correct) when you start the car in diagnostics mode, a lot of the sensor inputs are ignored, and the ECU operates under "default values"

its definitly something you need to do to set the base timing, (meaning the diagnostics mode stops the ecu from adjusting the timing)

there are ways to test a CTS. however given their price. i probably would just swap it given what i have seen over the past 2 years... (adding 2 to my shopping trolley )

[Sailbad_The_Sinner]

Thanks for the replies, gents, and apologies for the delayed acknowledgment. I used to get email alerts to post replies (or thought I did) but don't anymore, so until I decided to check my post this morning I thought I was being ignored, which I wouldn't blame you for. Is there another little box somewhere I need to click on to activate this feature?

I also have a great vanity plate pic I wish I could add as an avatar but all my attachment upload attempts get blocked...

Anyway I guess I'll start by replacing the temp sensor and will keep you posted. Also added my location and appreciate that tip too!!

[LightningFast]

Dave, don’t replace the ECU yet. Cold idle surge usually means a dirty idle air control valve or a faulty coolant temp sensor messing with your fuel mix. Clean the throttle body, check those sensors first. The oil leak won’t cause stalling but fix it soon. Focus on sensors and cleaning before tossing parts.

[Sailbad_The_Sinner]

Well mates I replaced the CTS and there's no improvement in the cold idle but now I notice a metallic rattle whenever the cold idle intermittently goes to wonk. My stateside friend @TorqueHorse thinks that might be the CAS; is there an Isuzu CAS equivalent that's a relatively inexpensive plug-n-play?

[Tuga2112]

you mention the issue is 'cold' 'idle'.
a CAS issue seems unlikely to only show its symptoms at cold and idle only. I would expect a CAS fault to be temperature independent and to manifest at the full range of revs. (specially at the higher end)

the next component that comes to mind is the Idle Air control valve. it controls airflow for idle operation, I've not read the book, but in my brain it makes sense to have different settings on cold and hot, but if it was stuck, it could (should?) also also manifest something when you drop the revs sudenly.

but since your focus is on the CAS
i would suggest to check the wiki page on it.
they can be repaired. theres kids, and as far as im aware. very dificult to get hold of a new one.
they are known to fail (reason why somebody has bothered to figure out how to repair it) but not a very common failure

just for reference, I cannot think of any confirmed case of a IAC valve failure, but i think someone replace theirs less than 2 years ago.. its a matter of using the forum search and finding out what other topics come up.

[Sailbad_The_Sinner]

Thanks Tuga. Just to clarify, I mentioned the CAS in the context of the metallic rattle only; not the cold idle issue. But I will investigate the IAC valve and appreciate the reply!

[TorqueHorse]

Agree with everything Tuga says.
I brought up CAS because maybe it got knocked when he changed the CTS, but agree with your comment about not being temp related, so could probably rule out.

alright, Dave just sent me a video and I've uploaded it here for people to see/listen to.
https://photos.app.goo.gl/CUfSb7LbDRcvsWBM9

I have not heard this sound before on mine, but to me it sounds like a bearing going out? I was racking my brain with where bearings are that might make this kind of noise and have, what seems to be, an impact on the idle/running of the engine.

My top guesses go to:

Idle pulley
Tensioner

after that I'm thinking anything that has a bearing that might put load on the engine?

Water pump
Alternator
PWR steering pump
AC comp clutch

What do you all think?

[dapinky]

Now, bear in mind that I'm deaf in one ear, so "noises" are different to me anyway....

.... and from a video I can't tell where it is coming from....

BUT

It sounds to me to be a rattle from the valve lifters, similar to what you get when the oil drains out of them having been standing for a while.

What grade of oil are you using? When was it last changed? How long has the noise been happening for, and has it got worse or stayed the same?

[Sailbad_The_Sinner]

I didn't know oil could drain out of hydraulic lifters, but anyway I've owned the car since June of last year and haven't changed the oil yet because I haven't figured out how to get under it, as stupid as that sounds. The front end is too low to use my ramps and even my floor jack won't fit under it (not that I'd lift it that way even if it did!). But I bought five qts. of 10W-30 and a filter and really need to get after that...

[Tuga2112]

on my computer, specifically the monitor speakers. which are very low quality.

that sounds terrible, i mean, scary terrible. i can see where you got the belt noise tone from. but i Certainly get the impression theres something else as well, and a completely ignorant gut based idea points me to the cams.

I would definitely start by doing what Dave said. see what happens,

putting a endoscope down each spark plug to see if theres anything different about one compared to the others would also be in my quick todo list, mostly because i already have one, and even tho the video qality is terrible. it would be good enough to get an idea if all pistons have similar wear.

if theres a drop in power, i would (mostly because of both my prior experience, as well as the fact i have a well equipped garage) check the timing belt, specifically the cams alignment, im saying that because, not long ago, i found my NA to have te exaust cam 1 tooth out of alignment, and many years ago my SE had a very rought idle, which was also due to belt being a few tooth out of alignment... i know its extremely rare, but based on a video from facebook form last week, it just comes to mind again.

[TorqueHorse]

oh wow, ok I listened again and what sounded like a constant screeching before, I can now hear the clacking as well. I guess a deflated lifter that gets pumped up once the oil is warm could give the symptoms described?

Wouldn't taking the valve cover off and running the engine (being careful to keep WELL away of any moving parts and lay some drop cloth to catch rouge oil spray) be the quickest/easiest way to pinpoint valve train issue (and see the quality of the cam lobes in the process)?

Also, Sailbad Dave mentioned before that the selling dealer said they had "replaced the cam bearings" before selling it to him. We don't know what that actually means they did since the engine doesn't have "cam bearings" per se, but a history of valve train issue doesn't seem out of place with the audio guessing of Pinky and Tuga...

[FunElan]

I didn't know oil could drain out of hydraulic lifters, but anyway I've owned the car since June of last year and haven't changed the oil yet because I haven't figured out how to get under it, as stupid as that sounds. The front end is too low to use my ramps and even my floor jack won't fit under it (not that I'd lift it that way even if it did!). But I bought five qts. of 10W-30 and a filter and really need to get after that...

The car is only liftable from the jack points behind the front wheels. Lift the RHS up first, under the sill. The jack stand will go underneath where the raft bolts to the chassis. Take off the front right wheel - it's the only real way to get to the oil filter.

My thought is....change the oil asap. It also does sound a bit like a belt driven tensioner sound too, like a bearing is going bad. So if oil change (and valve train inspection) doesn't change anything, then it's time for a timing belt next perhaps?

[dapinky]

There area lot of things it "may" be, and I would be trying to narrow down all of the suggested items on a list, in whatever way I can get at them.

First, I would get hold of some instrument to listen to noises - I am fortunate enough to have a medical stethoscope which has the advantage of blocking out ambient noises, and concentrating on where the 'sensor' is held.... without one, I have used a metal bar as a 'sounding rod' and if you stick a 6" bar into a length of hosepipe which you hold to your ear (in my case, the left one ), and then place the free end of the bar against the item you need to examine, it should help to isolate exactly where it is coming from - bear in mind that it may not be a single point, and there could be more than one issue - but you have to start somewhere!

I would place the bar against the following items to see what I can establish as a potential problem:-

1) Alternator - you will hear if the bearing is bad, or if the belt just needs adjusting (if there is a screech, try loosening the belt and see if it goes away)
2) PAS pump - same again
3) AC compressor - if fitted - same idea

If any of those are making a noise, simply remove the belt and see if the noise disappears - if so (or it diminishes significantly) then you have found the problem, or at least, some of it.

4) Timing cover at various points to see if you can isolate any noise to the tensioner, idler or waterpump
5) Valve cover - at as many points along it's length (for both cams) as you can - this may help to decide if it is valve clatter (lifter) issues, or cam bearing(s)
6) CAS housing - there is a bearing in the unit which can go bad, but is replaceable with some care.
7) Bellhousing - it *may* be a clutch issue... but this is pretty rare on these engines

After that, it is (unfortunately) a case of getting to the parts identified, and seeing what is out-of-spec and needs attention.

If you can't get under the car at the moment, but still feel that you want to try to mend something, then the valve cover can be removed to see if the cam bearings are bad, and the cams can be removed (having taken off the timing belt top cover, if you can without needing to lift the car) - and marking the pulleys/belt to refit in the right place. Then you can remove each valve lifter and check/clean/refill each one....... there is a short video on the Manuals page of how to do it.

If you suspect that it is a valve lifter or cam issue, then an early oil change should help to address it - even if it doesn't disappear, it should diminish, and after a shortish drive (half an hour is usually more than enough), it should be almost gone..... but if it is a camshaft bearing, then it may take more work!

[Delaneycatz]

Good morning. Just jumping into the orginal issue I’m having a simular if not different issue. Starts on the turn of the key every time when cold but my problem is that until the engine has warmed up a little the moment you give it some gas it dies straight away. Once warm no issues. Would this likely be the air idle valve or is there somewhere else I should be checking. Thanks in advance for any direction.