1990 Volvo 240 engine idle shuttering problem

I recently purchased a 1990 Volvo 240 at 108k miles and when I purchased it, the engine was pretty smooth running but shuttered around every 5 seconds where the engine would shake noticeably (not violently). There has not been any startup or running issues so I assume getting it back to stage 0 would get rid of it (as car had no maintenance record).

So I did the following maintenance (as well as others not listed):
synthetic oil/filter change
cleaned engine during oil change with Seafoam
cleaned fuel system with Seafoam and later with Techron
new gas filter
new air filter
new NGK iridium spark plugs
new ignition wire set
new distributor cap and rotar
cleaned mass air flow sensor
cleaned throttle body (very dirty) and replaced with new gasket
new o2 sensor
new flame trap (not plugged up or on any of the hoses but pretty dirty)
new fuel pressure regulator (no gas leak but strong smell of gas in hose)

I then cleaned the idle air control with carb cleaner and the shuttering got a little worse with a more noticeable half a second of hunting. But with my recent tach gauge installed, the idle is good, but will see it going from 700-800 rpms when it shutters.

I'm currently getting about 25 mpg on 80% suburbs and 20% highway so that is fine...and working on improving it.

As I am not an experienced mechanic, need some help? Do not think it is CPS or TPS? Done a lot of research but just cannot pinpoint what might be the caused.

Appreciate any suggestions or should I assume that I'm already doing good with a 25 year old car?

Thanks all.

Check for vacuum leaks if you have a hunting idle.

Do you ever get a "intermittent crank signal missing" code? Wiggling CPS wiring does anything? If not, probably TPS or cable/TB linkage... TB set to spec?

Vacuum leaks are also a possibility...

Thanks guys for responding.

Forgot to mention and to be more precise, the shuttering is erratic. It is not every 5 seconds, sometimes, 2,3,5 seconds. And forgot to mention that fuel injector o-rings are new as well.

It's an NA and I have checked all the hoses for cracks/worn/leaks and fixed larger or changed the smaller ones with silicon hoses. (I had some left over from my previous Saab 9-5 Aero. That turbo was very sensitive to leaks.) Nevertheless, there are not that many vacuum hoses to check for NA, right? Are there any specific ones that are more prone to leaks that cause this problem that I should check again? I think I carb sprayed all the hoses and nothing.

Do not have check engine light on, should I still check for codes?

Before I cleaned my TB, I read up on it and it noted not to make any adjustments (unless you know what you are doing) so did not touch it. How do I know if my TB is set to spec?

Or if the cable/TB linkage is correct? I assume that that is the wire with 2 plastic sheath for the metal ball/circular thingies (sorry, not in front of car). I tighten it but not too tight where I can still wiggle it some. Same thing with throttle cable, tightened but not too tight where there is still a little play when I press on the cable. If these 2 are set incorrectly, wouldn't that affect my idle to be higher if they are too tight opening up the butterfly?

The accordion hose inbetween MAF and throttle body is kind of prone to leaks.

You mentioned TB was very dirty, but it would still run fine... Dirty TB would make it idle low...so everything tb related might have been tampered with.

Go over this:
https://www.volvoclub.org.uk/faq/En...rottleBodyandThrottlePositionSwitchAdjustment

Thanks guys, will take a look at the accordion hose. It seem pretty solid when I was checking the hose to flame trap and IAC, and the ends to MAF and throttle body seem fine too...but I did not really take it out to inspect if there were no cracks between the creases.

When I got the car, it had no tach so did not know the idle when it was dirty. After all the cleaning did I install the tach and it was moving between 700-800 rpms. So it could have idled low beforehand.

Went through the link and also reviewed on Bentley and will check to see if everything is under spec.

I have a road trip so hope to get to it when I am back next week...and let everyone know the results.

Cheers!

Finally got to checking on the the possible solutions.

Took out the accordion hose and closely examined all edges/hose connections/in-between ribs and no cracks/holes that I can detect.

I checked as per link that the TB is within spec. No issues. However, notice that the TB has noticeable oil/grime on butterfly area even though I clean the TB about 6 weeks ago. Is this normal? As mentioned, I clean my flame trap and having checked it again, I see it catching some grime.

As noted, no check engine light.

Any other suggestions?

Thanks.

Have you figured this out yet?

I'm having pretty much the same problem with my '92 245.

I started it up after putting new brakes on and changing the plugs; it had sat for a few months. At first it stumbled a bit and I had to keep the rpms up a little but eventually it seemed to idle fine except for an intermittent miss. It seems like a slight hiccup and you can hear it most out of the tail pipe with a small puff over the consistent idle. It revs up fine with only a very slight hesitation. Pulled the AMM plug at it wanted to die immediately, so that seems to work.

Now I have not done any of the maintenance items like you have, but I plan on doing all of it asap.

Can anyone chime in?

Back from the dead... sorry.

I am having the exact same issue with my '92. It drives fine and gets decent mileage, but the idle sucks. It sits right around 900 RPM at idle with A/C turned off, but shudders every few seconds at idle, though there is no major change in idle RPM when it shudders. It's got newish NGK copper plugs, new wires, new cap/rotor, new FPR, clean flame trap, new OEM motor mounts, new Bosch main fuel pump, and no holes in accordion.

The only other symptom is a very low idle when the car is started. For the first 2-3 seconds, it idles around 500 RPM before stabilizing at around 900 RPM.

WhiteT5 said:

Back from the dead... sorry.

I am having the exact same issue with my '92. It drives fine and gets decent mileage, but the idle sucks. It sits right around 900 RPM at idle with A/C turned off, but shudders every few seconds at idle, though there is no major change in idle RPM when it shudders. It's got newish NGK copper plugs, new wires, new cap/rotor, new FPR, clean flame trap, new OEM motor mounts, new Bosch main fuel pump, and no holes in accordion.

The only other symptom is a very low idle when the car is started. For the first 2-3 seconds, it idles around 500 RPM before stabilizing at around 900 RPM.

Click to expand...

Have you cleaned your throttle body and/or adjusted the TPS?

TempleUWS6 said:

Have you cleaned your throttle body and/or adjusted the TPS?

Click to expand...

My car is LH 3.1, so the TPS is not adjustable to my understanding. I've looked at the throttle plate and it doesn't seem very dirty... just a very light layer of grease/grime.

I'm thinking about sending my fuel injectors off to be professionally cleaned. Seems like something easy to try for $50.