polarKALOS

A french speaker asks me to see if I may post here about a problem, which perhaps will help others searching or gather a response. All useful experience I hope, including for Aveo owners. He has bought a used 2008 model KALOS manual transmission with petrol/gas combination that behaves erratically. I hope the technical progress helps other readers.

When he drives (engine warm) and slows down shifting gears and declutched the engine rpm drops from, say 3000 to 1800 then swiftly surges up again once or twice to 2500 then drops like a stone and usually stalls.

If he stays in gear to slow down, foot off the gas pedal, the car slows a bit then suddenly accelerates toward the traffic in front requiring hard braking to prevent. The control of the throttle position seems miscalculated by the computer.

When cold starting it often stalls or during the first two or three parking movements. Reading others' experiences the indications are of an airleak somewhere. Here's what he's already done (with help).

Replaced the MAP manifold air pressure sensor with spare part. No change.

Test drive without the MAP connected. Engine control movement becomes smooth and normal and the car a bit more powerful too. It can stall yet far less or often not at all. Engine alarm on yet the tech detail in english on the CD mentions that without the MAP the computer chooses TP Throttle position mode and can still drive. There's no detail to say if the TP mode is only looking at the throttle lever angle to calculate a crude injection of fuel or whether it's some useful backup data on pressures due to throttle position and engine revs and temperature (some sort of intelligent estimate). No idea of the long term effects on emissions or performance/economy so he continues to investigate for a leak.

Switching to GPL liquid gas system gives the same results so probably not a fuel pump nor fuel pressure issue.

Investigated the EGR valve. Quite clean, zero alarms and he added a cover plate of thin metal to block it off completely to exclude any leaks from that circuit for a short test drive. No change.

Checking for airleaks. Using lighter gas cannister and inspection all tubes and hoses and connections have been tested up to each accessory (including brake assistance servo) for airleaks into the inlet system, including the few non-return valves and all seems airtight - so only the plastic air manifold itself and it's bolting to the cylinder block behind remain untested. Overall the engine running makes a powerful draw of air with good braking too. No change to the original problem.

Dismounting the throttle body reveals a bit about how it works yet it were clean already (as if new or replaced). Air filter body and inlet tubing inspected apparently super clean and airtight.

When testing the throttle action inside the car, choosing 2500 rpm (MAP connected, normal configuration) it matters not whether he keeps the gas pedal at a fixed position (same thing using the hand), the throttle controller forces a reduction bit by bit (you can feel the cable click or jumping slightly as the engine butterfly control motor does different to the requested setting) and slowly but surely the engine speed drops then stalls.

No other alarms nor problems indicated, no idea yet of fuel consumption although he's doing a test now.

Spark plugs seem new and perfect colour/combustion and when the car idles it stays steady at about 700 rpm.

The learning procedure for the idle for use in a garage (ignition on 5 secs, off 5 secs, start up, warm up, aircon on 10 secs, off 10secs, on 10 secs, off 10 secs, stop engine, restart). On a few occasions during that procedure the engine revved up high to 1500 rpm then reduced yet after the procedure the idle at rest is correct with aircon off or on, as if the system has learnt correctly a stable speed and control.

For the moment he drives with the MAP disconnected in what daewoo call the TP mode to have a safer experience in most traffic.

thankyou for reading; I hope complete information is appreciated and the owner will get an emission test without MAP in TP mode in the next few days. Considering an airleak can be a lengthy investigation he hopes to have made some efforts before suggesting a garage starts replacing parts all over. By the way there's indication the vehicle did hit something in the past (radiator bent, slight damage under front wings) and that the master brake cylinder were replaced (looks brand new compared to the very slight dustiness of the rest of the engine space) and if someone were to have attempted to brake, either it's plausible they heard nothing (because the KALOS is very quiet and engine stall is not much different in noise levels) had no servo assistance without realising that were the cause; in other words it seems the brake servo has been replaced after a minor accident without investigating the real cause before.

In TP mode it's less than risky to drive - seems quite good actually. Any comments or encouragements appreciated.

regards
PolarKALOS

polarKALOS

Progress

Stalling and surging problem solved the tappet clearances had been ignored by previous owners expecting the usual hydraulic system. This model vehicule 1.2 has manual adjusters and maintenance schedules specify regular inspection (every 10 000).

Without mentionning need to adjust the Daewoo guides imply little need to adjust. However for a vehicule running also on LPG or mostly on LPG some sites suggest the valves recede into the head causing unusual idling, stall, running problems which are either solved by adding lubricants to the LPG circuit (which runs the cylinders cleaner and without the oiling achieved with petrol) or checking if a particular model is vulnerable in the long term before buying it secondhand.

CO emissions high not yet solved. This may be due to the rich mixture average or something else. Today the car goes for a new timing belt and it'll be looked at again (discover if the catalyser or other units have suffered some damage due to the previous problem above)

cheers
polarKALOS