Well as the title says, I got a new IAC for my 240 automatic, thinking my old one might be kinda lazy off idle sometimes. I've been trying to track down a pop/hesitation on acceleration from idle, only when the car is still cold. Replaced coolant temp sensor, checked for vacuum leaks, replaced throttle position sensor and MAF, replaced fuel injector gaskets, etc.
The hesitation has been consistent since I got the car, but one time I was tired and was replacing the fuel pressure regulator, and BAM, the car caught on fire upon restart because I forgot to tighten the fuel rail properly. Anyway, I got my fire extinguisher and put it out, only to find that I needed a new tubing from the air filter to the intake manifold. The pops started at that time. I replaced that, as well as any singed wiring, and there was no change in the popping/hesitation. I checked for vacuum leaks and replaced a ton of parts/stuff, except not the IAC. I figured maybe it fried my IAC, and after cleaning it, still have a pop/hesitation when the car is cold, not when the car is warmed up. I also have the hesitation particularly bad if the car is timed (distributor timing) to 12-14 degrees, so I timed it at 20 degrees with a timing light. This makes the hesitation almost completely go away and almost never pops, even when cold. The only thing is, I MUST use high octane fuel or else it pings. Maybe the IAC is creating a lean condition when it's cold, not fully closing or something? The mechanic who had it previously, who I told about the problem, seemed to have rigged the throttle position sensor and throttle plate to be open at idle, past the click that the throttle position sensor makes after slightly opening, which means that the throttle position sensor would never have engaged the IAC (Due to not being at resting position). This makes me think that he suspected the IAC as well, and just bypassed it to compensate for a lazy IAC by not allowing it to engage at all to begin with.
Well, I got a brand new IAC from Swedishcarparts, and then installed it. The new one did not work AT ALL. It gave me a high idle, like 3k rpm, no matter how many times I unplugged and plugged it back in. I replaced it with the old one and that worked fine, lower idle that when revved, does have a little rev hang but does also return to normal 800rpm or whatever.
Any thoughts, ya'll? I sent the IAC back to Swedishcarparts and the tech out there told me he tested the part and it works fine. He has suggested that maybe the plug didn't make contact with the terminals completely due to the new part being slightly different than the old part, and that I need to like slightly bend the terminals to compensate or something. He said it worked just fine for him, no problems. I'm having trouble believing that, as I did bend the terminals slightly after first installing it and finding no response from the IAC when plugged in. They will be sending me my "fully functional" IAC back in the mail...
New 1986 240 IAC Not Working?
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122sPhil
- Posts: 43
- Joined: 21 September 2025
- Year and Model: 1966 122
- Location: Vancouver BC
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id bench test the thing before spending money. its only two wires on a 240 or my 89 anyway and threewires on my 88 740. its a different part,
from what I found it never completely seals, there is some blow through but more when open.
I cut one open to see inside,it was reported to be a motor" how is this a motor I thought?
well it is a motor but its the only motor Ive ever seen that can;t complete a revolution , it only turns part way pening or closing the valve. I also saw no sighns of wear or reason why it shoud have been replaced.
suggestions, do a smoke test, inject smoke into the manifoild to look for leaks.
check the flametrap, thats a plastic box, it can be removed without remving the manifold.
it can crack, also check that the screen in the hoise mear the flame trap is not pliugged that blocks the vent and can increase crankcase pressure, Ive seen it blow out a dipstick it can blow engine seals. you can replace it I cleaned them before if I didnt have one handy , thats fine
next Id verify if your air mass meter is working properly, mine wasnt and I relictantly orderd an offshore one , it helped a lot but when I installed it it needed some adjustment, thye have an adjustment some are covered up by a plug, also the wires to it can corrode so check the connector.
Id run it a while wiht fresh plugs and them pull them to check the iar fuel mix, mechanics may heva better tools to verify the AF mix is correct, but look at the color of th eplgs , it s an indicator we all have.
if you wan tot watch wen it closes or opens you cna hook iup a lamp or two, use small lampos so you arent; causing an overload then you can see when its open and wheni ti s not ot when it is electrified and when it is not.
I believe it is the same ECU used in both my cars so how one uses two pins and the other uses 3 pins is a bit of a mystery to me... and not all years and models share the same ECU there is atable somewhere that lists them , turbos need a different ECU but I have no turbo cars, just nore to go wrong and fix in my opinion. yes a bit more power..
I replaced the one in my 240 it did not make a lot of difference that I could tell.
id bench test it its not hard to remove and its not hard ot connect 12 V to check it is responding..
the volvo tune up booklet says to check its resistance, you can probably follow that and verify its resistance is correct to the volvo specs.
id add that my 740 had a rough idle I dint know why that was, one day I got out and just adjusted the air bypass to increase idle a little it seemed ot make a big difference.
you mentioned timing, the car has a knock sensor, you can check it. what I saw on a video yeasterday the guy put it in a vice with a meter or scope coected, he gave the vice not the sensor a hit with a hammer making it "ring" they sense the frequency.
the idea is they retard the timing when it hears this pinging ( before you can) and adjust the timing to prevent knocking..
if that was bad or had a bad connection maybe that could cause it to ping particularily on hills
an old method of settign timing pior to the knock sensors was to drive up a hill and advance timing until pinging could be detected then back it off a little.
i tend to run higher octane fuel when available, my feeling is that if the pinging doesnt ocurr and the engine doesn;t need to adjust its timing it is probably running more efficiently bu tIll leave that to question. Ive also heard its akin to buying shoes that are too big hoing to run faster so you decide..
low octane fuel pings more easily so I would think it is retarding the timing more often then. and altitude has a role in all that too.
if you have a spare knock sensor its easy to swap as a test, see if you see a difference, i havent heard of them coming loose but that could be possible.
you can check fuel pressure with a guage Im in the process of making up an adapter neither of my cars have a port so Ill cut a fuel rail and a fuel line form spare parts ad make a Tee, when I make that tee I plan to also make enough hose in my rig to connec the guage but also to reach out of the engine bay, why so I can fill a gas can and check that th epump is able to supply enough fuel, if the filter gets plugged it can cause fuel starvation ,
im workign on a 740 I had sitting a while a few years. the filter was totally plugged, also the in tank pump was bad.
if the in tank pump fails it may run fine until its about half a tank then struggle to get fuel the main pump then starves for fuel and I guess it cavitates. ( the fuel boils at room temp ata low enogh level of low pressure) you can think of a vaccum but the term "vacuum" is technically a bit confusing if you account for standard air pressure..
you can check the in tank poum by filling a gas can from the line that feeds the main pump it should be moving a considerable amout of fuel
if the fuel pressure regulator ails , it has a diaphram if the diaphram ruptures you may smell fuel in the vacuum line that leads to the manifold, there should be no fuel in this line.
the best way to check fuel pressure is ot adapt a guage , I dint find an easier way than to sacrifice an old filter to fuel rail line and the end of an used fuel rail to obtain the fittings but you can likely buy an adapter, my guage didnt have one.
i believe after around 91 or 92 or so it may have had a fuel guage port so have a look if yours is newer than about an 98 it may be there. some cars use a Shraeder valve ( spelling? ) lets say a tire valve,,
I ma not a volvo mechanic and if some of this sounds "off" then feel free to correct me, im not that techincal so its mostly just from my experiences.. takit all with a pinch of salt but maybe some of it helps.
from what I found it never completely seals, there is some blow through but more when open.
I cut one open to see inside,it was reported to be a motor" how is this a motor I thought?
well it is a motor but its the only motor Ive ever seen that can;t complete a revolution , it only turns part way pening or closing the valve. I also saw no sighns of wear or reason why it shoud have been replaced.
suggestions, do a smoke test, inject smoke into the manifoild to look for leaks.
check the flametrap, thats a plastic box, it can be removed without remving the manifold.
it can crack, also check that the screen in the hoise mear the flame trap is not pliugged that blocks the vent and can increase crankcase pressure, Ive seen it blow out a dipstick it can blow engine seals. you can replace it I cleaned them before if I didnt have one handy , thats fine
next Id verify if your air mass meter is working properly, mine wasnt and I relictantly orderd an offshore one , it helped a lot but when I installed it it needed some adjustment, thye have an adjustment some are covered up by a plug, also the wires to it can corrode so check the connector.
Id run it a while wiht fresh plugs and them pull them to check the iar fuel mix, mechanics may heva better tools to verify the AF mix is correct, but look at the color of th eplgs , it s an indicator we all have.
if you wan tot watch wen it closes or opens you cna hook iup a lamp or two, use small lampos so you arent; causing an overload then you can see when its open and wheni ti s not ot when it is electrified and when it is not.
I believe it is the same ECU used in both my cars so how one uses two pins and the other uses 3 pins is a bit of a mystery to me... and not all years and models share the same ECU there is atable somewhere that lists them , turbos need a different ECU but I have no turbo cars, just nore to go wrong and fix in my opinion. yes a bit more power..
I replaced the one in my 240 it did not make a lot of difference that I could tell.
id bench test it its not hard to remove and its not hard ot connect 12 V to check it is responding..
the volvo tune up booklet says to check its resistance, you can probably follow that and verify its resistance is correct to the volvo specs.
id add that my 740 had a rough idle I dint know why that was, one day I got out and just adjusted the air bypass to increase idle a little it seemed ot make a big difference.
you mentioned timing, the car has a knock sensor, you can check it. what I saw on a video yeasterday the guy put it in a vice with a meter or scope coected, he gave the vice not the sensor a hit with a hammer making it "ring" they sense the frequency.
the idea is they retard the timing when it hears this pinging ( before you can) and adjust the timing to prevent knocking..
if that was bad or had a bad connection maybe that could cause it to ping particularily on hills
an old method of settign timing pior to the knock sensors was to drive up a hill and advance timing until pinging could be detected then back it off a little.
i tend to run higher octane fuel when available, my feeling is that if the pinging doesnt ocurr and the engine doesn;t need to adjust its timing it is probably running more efficiently bu tIll leave that to question. Ive also heard its akin to buying shoes that are too big hoing to run faster so you decide..
low octane fuel pings more easily so I would think it is retarding the timing more often then. and altitude has a role in all that too.
if you have a spare knock sensor its easy to swap as a test, see if you see a difference, i havent heard of them coming loose but that could be possible.
you can check fuel pressure with a guage Im in the process of making up an adapter neither of my cars have a port so Ill cut a fuel rail and a fuel line form spare parts ad make a Tee, when I make that tee I plan to also make enough hose in my rig to connec the guage but also to reach out of the engine bay, why so I can fill a gas can and check that th epump is able to supply enough fuel, if the filter gets plugged it can cause fuel starvation ,
im workign on a 740 I had sitting a while a few years. the filter was totally plugged, also the in tank pump was bad.
if the in tank pump fails it may run fine until its about half a tank then struggle to get fuel the main pump then starves for fuel and I guess it cavitates. ( the fuel boils at room temp ata low enogh level of low pressure) you can think of a vaccum but the term "vacuum" is technically a bit confusing if you account for standard air pressure..
you can check the in tank poum by filling a gas can from the line that feeds the main pump it should be moving a considerable amout of fuel
if the fuel pressure regulator ails , it has a diaphram if the diaphram ruptures you may smell fuel in the vacuum line that leads to the manifold, there should be no fuel in this line.
the best way to check fuel pressure is ot adapt a guage , I dint find an easier way than to sacrifice an old filter to fuel rail line and the end of an used fuel rail to obtain the fittings but you can likely buy an adapter, my guage didnt have one.
i believe after around 91 or 92 or so it may have had a fuel guage port so have a look if yours is newer than about an 98 it may be there. some cars use a Shraeder valve ( spelling? ) lets say a tire valve,,
I ma not a volvo mechanic and if some of this sounds "off" then feel free to correct me, im not that techincal so its mostly just from my experiences.. takit all with a pinch of salt but maybe some of it helps.
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