1998 V70 GLT surging idle when warm

jgerhard45 · Post by **jgerhard45** » 24 Dec 2010, 13:43

I have a 1998 V70 GLT with 277k miles. The engine runs great and has 180 psi compression in all cylinders. It has a problem of the idle surging severely when completely warm. When starting cold with the check engine light cleared and the IAC plugged in it runs fine and all the OBD parameters are in range. When it gets to a certain temperature it sets a check engine and the idle surges severely and goes to open loop. If I disconnect the IAC it goes back to closed loop and runs fine except for a high idle. I’ve seen this exact problem described on the web with this year and model but no one seems to have a clear answer to fix it. I have tried a different IAC, ECU and crank angle sensor. I have recently replaced the MAF, thermostat, coolant temp sensor and radiator. The coolant temp sensor was bad and reading about 20 deg. F too high but replacing did not fix the problem. Any help would be appreciated.

Post by **Ozark Lee** » 24 Dec 2010, 13:54

Welcome to MVS,

It sounds like you have already thrown most of the usual suspects at the problem. You indicate that it sets the CEL - what code does it report?

...Lee

jgerhard45 · Post by **jgerhard45** » 24 Dec 2010, 14:53

It sets P1505 and P 1507. I did a test awhile ago and found the coolant temp while driving regulates at about 198 F with the new thermostat. When I stop and idle the temp goes up to about 216 F, at that point it trips the CEL and starts the idle surging. If I let it cool down a bit I can reset the CEL and it runs fine. The codes mentioned are the IAC high and low signals. The IAC is trying to control the idle but it can't. The fan is turning on but I'm not sure if it does at the right temp.

Post by **jblackburn** » 24 Dec 2010, 23:02

I would look closely for an air leak somewhere. It sounds like the IAC is having trouble regulating once the O2 sensors start reading at idle. Start with the turbo hoses - they like to blow off the clamps sometimes and cause odd running problems; then check over the vacuum hoses.

drjohnson666 · Post by **drjohnson666** » 14 Jun 2021, 05:01

Hi, I know this is an old post but I'm having simialr problems. Did you ever fix what was causing the P1507 ? Yours Dave

JoebobNLacey · Post by **JoebobNLacey** » 16 Feb 2026, 18:35

I realize this is a REALLY old and short thread, but have the exact same thing happening to my 1998 V70 T5 right now. I'm going to start a new thread in the search for help with a few more details, but will still post to this one too.Car has surging idle. Eventually and finally threw code 1505. I swapped out the IAC valve with a spare and exact same thing is happening, only when at full temp. Temp gauge on dash looks normal, but something smells hot. OBII scanner suggess engine temp is around 230, which seems high. Once at full temp, idle speed stays at 1300rpm, surges to 1500rpm within a few seconds, drops back to 1300rpm. Never dies or stalls, drives great otherwise.

Post by **Grantkat** » 21 Feb 2026, 07:37

Take a look higher in this thread. check for leaks as descibled above.
Check your vacuum lines
checks your turbo hoses

if you have a leak somewhere it could manifest issues like you describe.